My 3G became dog slow as a dog when I installed the software that was released alongside the 3GS. It has been ever since, through every following upgrade.
I noticed my 3G seemed to start getting slower, have more frequent "world has come to a stop" pauses right around when the 3GS came out. I wondered a bit if it was a conspiracy of sorts, something intentional Apple did to make the non-3GS models seem even slower than they were. Not sure, of course, or whether a coincidence. But it's interesting to hear at least one other person noticed this.
