I'm running 10.5.2 on a 2x2.66 GHz Mac Pro with 5 GB of RAM. I bought this system last August and have never had even the slightest trouble. However, in the past week or so, the computer drastically slowed down. This is most noticeable in video playback- anything I try to play in VLC (regardless of resolution) ends up dropping frames and gives me a message about my CPU being too slow. Also, I can't even watch a Youtube video without dropping frames. I use Firefox, and if I have several tabs open at once, it responds very slowly and there is a noticeable delay when switching between tabs. Logic and Aperture are both noticeably slower as well, and during playback, the audio in Logic will occasionally drop out. I tried repairing permissions and that didn't help. Since it got to the point that I couldn't even us the computer without being frustrated, I did a clean install of 10.5, ran the software updates, and am now having exactly the same problems. I ran the Apple hardware test that came on the system DVD, and it reported no problems. So, I'm at a loss...do any of you have any suggestions? Also, I hadn't installed any new programs or anything that could have messed things up- it just decided to slow itself down, which makes it all the more perplexing.