Friends, I am having the same issue but can shed a little more light using my situation as an example: See my signature for the programs I have installed. Recently I have upgraded to B&W v1.29 (might be the issue). Space free, out of the 63MB that I have on my 8800, I usually have about roughly 36MB+ with all apps installed. The only issue I think is the B&W, ideaMatrix, todoMatrix, all run in the background, eating up tons of memory if you do a lot in the program(s). I really dont want to reload my OS because I normally dont have any freezing/restarting issues. So I am going on the assumption that I may have too many programs utilizing my data connection maybe, or swapping too much memory and not letting go.
EDIT: Worth nothing that I found this while searching (Blackberry freezing issue
) Maybe programs running in the background, along with other data services (syncing on email (i have gmail imap enabled)) could be causing this random bursts of rage from my berry as well. Not only are your messages open but the browser as well - FYI.