Joe has a Dell Inspiron i7 and it slows down a lot. He's found that the best way to speed it up is to reboot, but he doesn't want to do that all the time. Leo recommends looking at his system's usage with Microsoft's Process Explorer. It could point to what applications are experiencing a memory leak. That's when programs don't release the memory when he's done using them. It could even be an extension running in the browser or Flash. It could also be a flakey hard drive.
Joe may also want to try reinstalling Windows from scratch. It could be a bad build.