While Photoshop CS5 makes it easy to mix colours in the application, it is no replacement for working with a traditional artist's palette. This is something that Adobe Color Lava for Photoshop attempt to recreate, and it does it rather well. The iPad app enables you to mix colours and swatches on your iPad and send them to Photoshop ready to use.
You can work with the app independently of Photoshop, blending colours on your iPad and making fine adjustments using hue and saturation sliders. Your creations can then be sent to Photoshop CS5 as soon as your iPad is on the same network as your PC or Mac that has the software installed. Adobe Color Lava can also be used to directly interact with Photoshop - tap a swatch in iOS to make it the foreground colour in Photoshop.
The idea behind the app is an interesting one, and it provides scope for a great deal of creativity - if inspiration strikes when you are away from your computer, you can start creating swatches wherever you may be. Your creations can be shared with others via email as well as transferring them to your own computer.
One problem that serious Photoshop users are likely to encounter is the fact that the iPad screen cannot be properly calibrated so it can be difficult to ensure that the colours you see on screen will look the same on your monitor or when printed.
An interesting idea that is well executed, but the lack of calibration of the iPad may be its downfall.