Originally Posted by Europa
^Updating to the new 3GS will take care of that problem, it's lightning fast.
Although I'm not experiencing the keyboard lag (just the home screen lag), I don't think it has anything to do with the differences between the 3G and the 3GS. I believe it has to do with the jailbreak, or possibly the combination of jailbreak and some non-appstore app.
Just for the record, the getting-to-the-home-screen lag doesn't happen every time, just about two-thirds of the time.