What sort of widgets do you have on your home screen?
When this delay happens, do you see a two circle arrows icon next to the 3G symbol on the top bar? This is an indicator that the phone is undergoing a sync at the same time.
Does your phone feel sluggish when you are experiencing this delay?
I can't recreate this exactly with my phones, so I would have to theorize the possibilities based on similar symptoms.
1. Complex screen widgets can cause delay. Try removing some widgets on the screen and see if the response improves.
2. A bit too much background syncing caused by services and apps. You have to lengthen the time intervals between syncs or reduce the number of syncs daily.
Are you using live wallpaper? Not likely to cause it what you're seeing though.
Possible disk fragmentation of the SD card. This slows down disk I/O, including caching of the UI.
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