I went with Carman for Nokia's Maemo platform and a generic Bluetooth scantool. The advantage of this setup is that the Nokia webpad serves as an in-car media player, GPS unit and car computer, providing me with real-time diagnostics, positioning and entertainment.
For fault diagnostics, I gave up in the end. At least for my car, (an Audi S8) it seems there are error codes that are manufacturer specific. Without a translation table, the error codes aren't particularly useful and I couldn't find any software package that included them or, indeed, just the Audi S8 code table. Happy to be proved wrong here if someone else knows better than I do..