Android OS versions breakdown
Well, this is an interesting info.
The newly released Android devices graph is based on devices, which have accessed the Marketplace within the last two weeks and will be updated periodically.
As you can see the 1.5 devices have a share of more than a quarter of all devices but the main target for developers should probably be version 1.6.Android 1.6 devices account for more than half the market.
But v1.6 smartphones do not share one and the same displays and they vary from QVGA up to WVGA resolution. Source