searched forums for days for an answer and couldn't find one. Found my solution and figured I'd pass it along. had a 2.2 device, but suffered from random shut downs. Went through 2 additional units, and noticed successive lag with each device in general homescreen switching, games, and tried all solutions I could find except rooting/lag fix. With my fresh new device, I went to 2.2 and experienced the lag. My original device had none and many other devices ran fine. Its the sd card. I had an external, since I put it in an external card reader, wiped it out, formatted the card and put it back in the device the phone runs lightning fast. 2.2 should have no lag at all, this this device doesn't. Give it a shot.
The reason why using an empty SD card smooth the global user experience is because the Gallery app scans the SD card for images to create thumbmails in background.This process can take a lot of CPU resources.
It's not suppose to slow down the user experience in theory but in practice, it often does.
One other way to have a smoother user experience on the homescreen is to use an alternative homescreen ... or Launcher as it's called on Android. Some of them are free, some of them will cost you money. The most famous alternate launchers on the Android Market are ADW Launcher and Launcher Pro. I used ADW Launcher (free) for months and now I'm using ADW Launcher EX ($3.15) because it's even better.
on both devices i was using launcher pro and was getting lag on touchwiz or launcher pro. My device runs smooth after the sd format. I know the thumbnails in the gallery are stored on the sd. What I never guessed is that each device will create its on gallery on the same sd card, and one device cannot read the others. Thereby causing lag within the device. There is no need for a captivate lag fix, mine runs very fast. There should be no lag, format your external sd if you have any homescreen lag. No launcher should have lag, even touch wiz.
I also hear of people buying the cheapest 16G card available and then complaining about the phone.
I recommended they get the fastest meaning an expensive brand recommended in photography stores and that fixed their problems.