I've supported IBM, Compaq, Gateway, and WinBook laptops in office environments over the years. Of the four, I would recommend IBM as the best quality. I know of a lot more older IBM's that are still going strong at five years old, while the others have been relegated to the old parts bin long ago.
Service for IBM laptops was always very good, but we had corporate service contracts. I don't know what it would be like if you were a "retail" customer and didn't have a service agreement.
IBM parts are well indexed and standardized. You can find them on eBay pretty easily. The design of the laptops is functional, and they are built to be serviced. Items that are known to be fallible are modularized, and don't require prying apart thousands of little metal tabs to replace - usually a few screws and a snap-in module.
That said, you do pay extra for the IBM name. WinBooks will probably give you more for your money, but are not as servicable. When components start to fail at three years or so, it's time to think about replacements.
I know Tom's pretty happy with the laptops he keeps getting from Dell, but I think they've had his computers more than he has in the last two years. Dell does not play very well with Linux, I have yet to find the specs for the motherboard sensors on my PowerEdge server.