If you are anything like me, you are using Firefox and a multitude of addons. The downside to all this it turns out is that not only does Firefox become a huge memory hog (it is not unusual for Firefox to be using ~400MB of memory) it also becomes very slow.
The one thing I found which speeds up Firefox no end was disabling the Firebug plugin. I use it a lot when editing the layout of this blog but those are only for short bursts at a time so I can easily disable it.
As for the memory usage, well we shall see..