Business users also have to decide for which purpose they want to use open-source software and how critical it will be to their business processes.

Free, community-supported versions are fine for testing or non-critical needs, but when the work is mission-critical, users say they are more likely to pay for enterprise versions of open-source applications.

Jeremy Cole, a co-founder of MySQL consulting vendor Proven Scaling LLC, says that sometimes this split development model can cause unintended problems. One issue, he said, is that businesses that need to rely on stable, mature code aren't always getting what they pay for.

At MySQL, Cole says, "they release the enterprise version more often than the community version". What that means is that "while enterprise users are getting fixes faster, they're essentially running untested code", he said.

Others share the concerns. Such issues are growing in importance as more large companies buy open-source companies, adding a boost to open-source software in enterprise systems. Sun Microsystems' recent acquisition of open-source database vendor MySQL AB is the most recent evidence of this trend.

The beauties of open source Bill Parducci, CTO of Think Passenger, which builds online communities for companies and their customers, says open-source code is important to his young company because it lowers technology costs and allows customisation of key source code.

"The concept of an organisation pushing out the code faster so their clients can get the code faster, I don't agree with that," Parducci says. "Customers can't keep up." Because of such pressures, Linux vendor Red Hat doubled the length of its new version cycles several years ago to better meet the needs of its customers, he said.

"Software is more stable and supportable when [new versions are] less frequent. There's no value in software that doesn't work predictably."

Parducci says he is seeing more examples of software that takes a "hybrid approach" between open source, closed source, functionality, risk and support. "At the end of the day, you need to solve a problem," he said. "I think we're finally over the day of people running up the hill with a flag of open source or a flag of anti-open source."

Think Passenger uses a host of open-source applications, including Red Hat Enterprise Linux, CentOS Linux, Iona Technologies' Fuse Message Broker, Jetty Web server and Terracotta's network-attached memory applications.

Parducci said he uses the paid enterprise versions of most applications so he can get expert support and the most stable code. With Iona, "they take it, they stabilise the releases, they package it together and put support around it," he said. "It's the same basic code as the community version with support and stabilisation. It's working out well for us."

Parducci said he looks at whether a prospective open-source vendor is trying to upsell to a proprietary version of its product or whether a proprietary version is needed to maintain full functionality with other products. "To me, that really becomes a red flag," he said.

"Are they supporting the open-source stuff just to sell me up to the other side?" Working with most open-source vendors has been satisfactory, he said, but there is room for improvement, particularly among the smaller vendors. Such vendors need to ensure "timely feedback and improved communities" so that business users can get the help they require, he said.

"I think it's still going through the learning and growth phase. People are still figuring out how to staff it."

Enterprise versions worth the cost Justin King, a systems administrator for the Human Neuroimaging Laboratory at Baylor College of Medicine in Texas, said he's found that community versions of open-source applications are adequate for his needs, but that buying enterprise versions often saves time because they are more developed and include useful administrative features.

King said he uses open-source applications from Red Hat, web infrastructure management vendor Hyperic and others. "In the enterprise versions, in most cases, the main thing is stability," he says. "You can live without having certain [new and improved] features. The absolutely most critical thing is uptime and stability."

"The best model to look at is Red Hat," King says. "They've got [the community supported] Fedora [version of Linux] and it changes frequently. Then there's Red Hat Enterprise Linux that's stable and supported [for enterprise users]. That's the correct model of enterprise open source as far as I'm concerned."

For mission-critical business users, "nobody in their right mind is going to rely on something" that doesn't have adequate support and stable releases, King continues. "They'll go with supported versions if it exists to run their business. At the end of the day, if something's broken and nobody on-site can figure it out... it's cheaper to call the support guy and choke him until he figures it out."

Gautam Guliani, the executive director of software architecture at New York-based Kaplan Test Prep and Admissions, a college entrance exam testing company, says he prefers to buy enterprise versions of all open-source applications used in mission-critical roles.

Using community-based applications in pilot projects and non-critical business functions is acceptable, he said, but if his company wants to use it, it will pay for the enterprise version to get the support.

More road-map direction

Kaplan uses a small assortment of open-source applications, including JBoss middleware, Red Hat Linux and Alfresco web content management software. Getting adequate and timely support hasn't been a problem in general, Guliani says, but getting future road map direction from open-source vendors can be tougher than with proprietary vendors.

"The development road map is not as thought out as much sometimes as we'd like with open-source companies," he says. "Some do it well, but for most there is room for improvement."

What open-source vendors offer to his business, he says, is lower costs for support, deepening maturity, code flexibility, "a much deeper level of transparency into the software products," and a higher rate of innovation.

"The releases tend to come more frequently" with open-source vendors, he says. "If they come too often, it can be a problem. At least if they're coming often, we can choose not to upgrade to a new release. Most open-source vendors have realised that if they bring out a new version, that they shouldn't drop support for the old one too fast."

What's happened, say analysts, is that open-source software has quietly become an integral part of corporate IT, whether through community-based or enterprise versions.

Raven Zachary, a 451 Group analyst, says companies don't even look at software as being open source or proprietary, but analyse it based on what will work best for them.

"I don't run into enterprises very often that would be willing to give up functionality," he says. "Enterprises are going to purchase technology that will allow them to do their jobs. Sometimes that means proprietary. Sometimes that means open source. Generally, large enterprises are going to make decisions about what is right for them regardless of whether it's open source or proprietary, based on value."

Donald DePalma, an analyst at Common Sense Advisory, says business users with large data centers are typically using enterprise versions of open-source applications because of their mission-critical requirements. "Individual rogue business units are using community-supported versions," he says.

"There are levels of open-source use," DePalma said. "MySQL is so widespread in use that it seems almost Oracle-like in its commercial viability, so users don't even see a distinction. I think we'll see more of this moving forward."