Good luck with that. The latest beta is horribly slow and unresponsive. I'd be happy to post a video showing my iPhone 3G (OS 3.0) and my iPod touch (2.2.1) running side by side, but the difference is absolutely night and day. Games take forever to load and the framerate is AWFUL, the Settings app takes three or four seconds to load, and another three or four seconds to select a menu item. So it takes, every time, at least eight seconds to do something as simple as toggle wifi. Now, eight seconds might not sound like a big deal, but in practice it really is. I can perform the same task on my iPod in about about half the time it takes on the iPhone. Half! Performance is awful throughout the OS. Even doing something as simple as scrolling through a gallery in the Photos app - on the iPod it's smooth as silk. On the iPhone it stutters - quite noticeably - when I scroll through the same gallery.
At least on the iPhone 3G, OS 3.0's performance is HORRIBLE.
Note: I realize that this is beta software. I really do. It doesn't change the fact that OS3.0's performance on year-old hardware is absolutely AWFUL. While I hope that they will correct some of the speed issues by the time 3.0 is publicly released, I think that anyone expecting great or even good performance is deluding themselves. The iPhone 3G simply does not have the power (CPU/RAM) to keep up with the OS now, to say nothing of games and other apps. The iPod touch (2G) will fare better, but that's because the performance difference is, as I said earlier, absolutely night and day. I'd be happy to put a YouTube video up in the next day or two to prove this, if anyone is interested.