I warned ~ 3 months ago about iPhone 3G and iOS 4.0 performance issues. So now I’ve tested 3G with iOS 4.1 – performance issues are largely fixed. I can safely say that it is finally worth a swim.
If I’m not mistaken, 4.1 will be available to the general public sometime next week. Of course, it won’t be the same as the three-year-old version 2.0 that came on top at the time as pre-installed on 3G, but compared to the 4.0.x versions, this one will at least be usable.