OpenStreetMap (OSM) is not only a great example of the open source methodology being applied outside software, it also started in the UK, which is something to celebrate.
Not that's its stayed there of course, as this crowd-sourced mapping system spreads around the world.
One measure of its success and maturity is the fact that a commercial ecosystem is beginning to form around it, just as happened with GNU/Linux in the mid 1990s. Here's an interesting hint of what's to come in this area:
Companies have been using OSM data in proof of concept implementations for some time. Recently though the examples have become more prolific and more public: see flickr’s use of OSM. Some businesses are starting to rely on OSM for parts of their product offering, for example Wikitravel uses OSM derived maps in their printed travel guides.
New start-ups like CloudeMade in the UK and Geofabrik in Germany are being founded and funded around the business model of providing services around OSM (see TechCrunch coverage of CloudMade funding). The exact revenues of these companies is unclear (and likely still negligible) but the general concept of providing consulting and value-added services around a free (and complex) asset is well entrenched.
This year’s acquisition of MySQL by Sun is only the most recent successful (and European) example. One certainty is that the recent explosion of interest in online cartography has lead to the development of an increasingly sophisticated “open source geo stack” that will pressure traditional GIS software companies.