Well my MacBook is pretty fine. But ofcourse if I treat him wrong, he won't work well.
If you keep your Computer on for days and days, it gets slower. I don't talk about the technical reason. However, my MacBook is running for 11 days and 1h 36m right now. Ovbeously, it was slow but when I logged out and logged in, it got more quicker. Swap was 3GB but when I logged out and logged in, they are gone and it's 512MB.
If you don't want to waste your time waiting for computer to boot, logout and sleep it. there won't be almost any swapfile left but it didn't take as much as booting computer.