I have a Macbook Air. I use it every day and take it with me pretty much everywhere. It's one of the original (old!) models, and recently it started getting hot, noisy and lasting under one hour on a full battery charge, so I thought I was going to need to invest in a newer model. I seriously thought it was on its way out, even though it looks new.
Then I stumbled across a few forum threads, spent 5mins tinkering, and my laptop is as good as new. Battery now lasts 4hrs again, it's cool and makes no noise!
Some people said to me on Twitter this morning that they would be keen on me sharing the links to the tips I followed, so here they are.
3. Make sure Word and iTunes are not running unless you need them to be.
And le voila! Point 1 is new to me. Point 2 is fine, as I don't really need it. And 3 is just a tip, but one I had never realised was important.
Hope this helps!