I've owned Toshibas, HPs, Dells, and IBMs - and I highly recommend the Thinkpad. Just got a new T42 about a month ago and I'm just happier than a speckled puppy. They just put a lot more thought into their product, and I've never had a problem with them falling apart. Great battery life. Lightweight. Durable. You can find faster laptops for less, but I don't think you can find better laptops at all.
I have helped a lot of friends with their Sonys and I would say STAND CLEAR! Too proprietary all around. A real pain in the @!% every time I come across one. My HP was good, but that was before they merged with Compaq. I don't have a very high opinion of the Compaqs. My Toshiba was good until it started falling apart - and the battery life sucked among other things. I will never buy another Dell EVER again. Two laptops and seven screens.