When the iOS 4.0 software hit the iPhone 3G, it rendered the 2008-design nearly unusable. The lag going from one function to the next made it an excruciating smartphone experience.
Users who wanted responsiveness had to downgrade back down to 3.1.3, (or sue Apple). The downgrade, however, wasn't an easy one that could be done without going behind Apple's back.
iOS 4.1 improved the situation somewhat, but it was still not as fast as 3.1.3. Now that iOS 4.2 is nearly here, some early users of the gold master build feel that Apple hasn't given up on the owners of the older phone just yet.
Tests by Tipb seem to indicate that there are further performance improvements in iOS 4.2 that helps keep the iPhone 3G from obsolescence for a little longer.
It's by no means a scientific test, but those who have used an iPhone 3G while on iOS 4.0 will be able to tell that 4.2 is much, much better.