Well, I have had an IBM 600E (366mhz), a Compaq 2145 (2400+), and now a Dell 8600 (1.6 pentium m).
The 600E is the best built, but old and slow now. The Compaq had major problems from the start, including bad battery life, HD problems, keys that don't depress, very noisy, and horrible wireless.
My new Dell is actually very very nice in my opinion. It is silent (effectively), its wireless is great, the screen is big and bright, its fast, it has a 4.5 hour battery life, etc. Now, considering it has a dvd+rw and ended up costing 800 bucks, I think it is amazing.
Anyways, I just wanted to comment since people seemed to go off on a Dell hating tangent. The build quality might not be as awesome, but considering you can get 2 dells for the price of 1 IBM, I think I know what to do. However, I do not deny the superiority of IBMs in almost all respects aside from price.