The problem I ran into with my old Dell was, when the power supply went bad, I had to buy a whole new system because it was built with propriatory parts. I couldn't simply replace the power supply because the motherboard had a Dell-only connection on it, Dell wouldn't sell a replacement part for less that it cost me to build a new system myself, and good luck finding a working replacement PIII board in 2005.
Now, for a laptop, I imagine they're okay. It's not like you can easily build a complete laptop on your own anyway. Me, I bought a HP, only because of the price. Unfortunately, when I bought it at Wal-Mart, I was told that they didn't have any extended warranty plans. Then it crapped out after 9 months and only had a 90 day warranty. (HD went bad. Bigger problem was it crapped out 24 hours after my Dell desktop died.) I am now aware of the fact that you *CAN* infact buy extended warranties from Wal-Mart's website for shit you bought in the store. So no matter what you get, make sure you're covered for a few years.