I have an iPhone 3g, and when I installed the latest update, OS 4, things seemed o.k.
Then I setup a lock code, seemed to work. that is until I couldn't get it unlocked! I know I was using the right code because you have to type it in twice to get it to work.
So I had to wipe my phone and install from scratch, which now I notice that my phone is slower than ever.
honestly, if they keep putting out bloated and problematic updates, I will switch to an Droid.