After the 10.5.2 update, and following graphic update, Activity Monitor pie graph showed most of my 4 Gigs of RAM used (depicted as Inactive - blue), which was very strange. So, I shut down completely. Then upon reboot, my RAM was back and available (in green). In fact, now it is strange that after launching numerous applications there is still not any blue "Inactive" RAM on the pie graph. Something must be going on with this. But the OS seems to work fine!