Try a battery pull. If you've been switching around themes alot, it starts eating away at your memory, even if the themes is not running. I always do a QuickPull on my phone after resetting the theme.
edit: rememeber, the plazmic 4.7 that was leaked was an early beta, themes now may not be exactly optimal for the storm
It CAN have something to do with the theme programmer as well, but so far i've found the battery pulls help. But I only download the really good ones, generally the guys who make the good ones know what they're doing :P