Ok, so I recently installed snow leopard 10.6.2, the newest update, and I must say the update process was seamless (even though there was a part where it said it would take 1 GB of hard drive space to install this update, which got me kind of annoyed). It restarted the computer, I was just logging in etc. until I started up iTunes. And this is iTunes 9.0.2 we're talking about, the newest version of iTunes. I opened up the podcast section because I saw that there were a number of new podcasts and I double clicked on a video to play. To my dismay, my computer utterly clogged up and the whole system became laggy. Wohoo, go iTunes 9... Speaking of iTunes 9 I don't like the new GUI, and it does not look the part when compared to quicktime X, with the supposed "marble" interface, the GUI of 10.6 is getting more and more diverse, or shall we just say, random.
Edit: Now that I look at activity monitor again it might have more to do with quicktime, but I'm not sure what is causing the problem as of yet.
Edit 2: I went to the apple support forums and I looked through a couple of threads and it looks like some other people are also having the same problem as I have. Link for discussion board thread Now that I've used 10.6.2 for a bit longer, the mouse problem seems to be gone, but the iTunes problem remains. Other than that, no big changes, I hope 10.6.3 comes out soon.