I received this notice yesterday for the first time. I tried moving apps to sd card, deleting apps, deleting text messages, and maybe a few other things. None of those worked. Someone posted in this thread to look at all apps and filter by size. I did this and Dolphin HD was the biggest (70mb) So I cleared it's cache and the notice went away and has not come back after a day of use. I think this notice can come up for a number of different reasons. But that was mine.