Another bug. I got this in the beginning when downloading lots of apps and then I started moving them to "media storage". DON'T do this as half of your programs will disappear. Restart the phone and that should fix the "low storage" messages from popping up.
first are you rooted? if so look for vm heap app in market and change vm to 48. i had same issue and changed my vm its at 32 i moved it 48 not only did i stop getting low memory but it improved my over speed.