I've noticed several times a day when I open certain apps, they reload as if they were running for the first time. The most noticeable one is my launcher, GO Launcher EX. I have QuickDesk set as my launcher, which chain then loads GO Launcher and several times a day GO Launcher has to reload and lags the whole phone while doing so. I also notice similar behavior with Handcent reloading several times a day.
I have freemem set to 25mb, no automatic task killers, or custom sysctl settings.