http://forum.androidcentral.com/t-ca...g-lagging.html

Link to show this is a fairly universal problem, Benson has given one useful solution, also file system problems on the microsd can also cause this problem, as was the case with this android phone in the above link, in fact in any device with SD cards this can happen. It's fairly easy to fix, power off, remove the microsd and check the file system and correct any errors.

laggy also happens to iphones for various reasons
http://forums.macrumors.com/showthread.php?t=1100825