I don't think anyone's had any problem with Khertan's home* applets (homememfree, etc.), as they stop updating when the screen is off, or when the home screen's not displayed. Some other applets are not so good, and memory leaks have been suspected at various times in various versions of various applets. The best way to tell is to disable them until things go back to normal, and then restore any that didn't make much difference. Applets (whether home or statusbar) are definitely the most likely culprit, though; it's just finding which applet.