Just a warning... If you'd like to hang around the #maemo irc-channel you can get kicked for saying overclocking is okay... Seems the oppers in that IRC-channel thinks the /kick argument is the way to have nice discussions..

edit; and by the way, after having run 900MHz on my N900 since I got it a month ago I just upped the max speed to 1000MHz... runs fine for me, and I'll bet OC'ing will not be what kills this thing..