Do you power off your laptop?)
gaoshan: I have a Macbook and after about a week of continuous, heavy, use (I do web development on it so I may have Netbeans, Terminal, a billing app, Safari, Firefox, a Virtual Windows XP environment, vim, Mail, iTunes, iChat and an assortment of taskbar apps all running full time) I find it gets quite annoyingly slugish. A reboot refreshes things. I have only 2GB of RAM so that is probably part of the problem as I end up with more paging out I probably should.