I will say this, Apple's marketing people are absolutely brilliant. On my 3GS I was able to do multi-tasking, had folders, etc, everything that the iPhone 4/IOS4 for 3GS was capable of, waaaaaaaaaay before the 4/IOS4 even came out. Because mine was jailbroken. However, the phone itself had to have the capabilites in the first place.
So sales for the 3GS start getting low, what's Apple do?! "Release" a great new software update! Wow! Sales went back up! They really are brilliant.
Even with that said, I still bought the 4 a few months ago. I refuse to buy a first gen electrical product haha. Too many bugs usually. Hell, there's still some bugs with the iPhone 4 (massive problems with it syncing to iTunes). Even so, I absolutely love my iPhone 4. It really is an excellent product.