The new OS (3.0+) adds more features which speed up the development (like working with the lists etc). On the other hand there could be (potentially) a lot of users somewhere still running OS 2.2.
Is there any place to look for statistics? Could someone offer an advice on the target OS for a new iPhone app scheduled for Christmas release?
Based on Admob data, adoption rates of the earlier SDK releases have been pretty good in past. It takes a couple of months to reach over 60% adoption. See Admob stats
On the otherhand, I just saw another Admob report, which indicated that iPod Touch users are more likely to buy apps and they are not that likely to upgrade.
However, I’d bet on 3.0 for Christmas market and next year, if you need something from 3.0 SDK.