So I tried a bunch of the solutions suggested here on my wife's Droid. She was having the problem since I forced the first froyo update. Launcherpro didn't help, disabling animations actually caused some weird effects on the dock, and the lag was still hanging out in the stock launcher.
Then I tried switching lp out for adw and things seemed vastly improved; the lag (for the moment) seems to be gone.
That said, as a lp user on my dinc, I don't have this issue and after playing with the two phone with the memory heap size showing, I wonder if it isn't a RAM issue In part. During the lag, the lp heap size is generally way low, like 5 megs versus a 10-15 when it's up and running. On my dinc it never drops like that, and sits around 20 megs. I'm still a novice android user, but could it be possible that the OS is killing the cached homescreens out of RAM forcing the launchers to recreate them each time? Just a crazy thought from a newb! In any case switching the launcher to adw made a huge difference, so of you aren't so heavily invested in lp, you may give adw or any other launcher a shot and see if it helps!