I agree with what TS said, i have a Dell XPS, its a cracking laptop though its getting old in the 'high tech' side of things now days. Still functions just like when i bought it, and trust me its had a hard life so far in general.
This laptop did cost quite alot when new, but has a metal chassis aswell, the build quality overall for a laptop i really do think is excellent.
While i do agree IBM make excellent thinkpads, i too do love most Dell laptops within reason, their bit better range are excellent, ive had experience with alot of Dell machines and unless seriously abused, the decent ones seem to keep on going on and on.
I used to fix all types of laptops a few years back, and have dealt with many, some of which cost well over a grand back at that time and the build quality of which were really rubbish, hence the reason most of them were broke / faulty.
Ive had experience of owning alot of crappy laptops over different periods of time too. If you want a solid laptop buy a Panasonic ThoughBook, the last ones of those i dealt with though it was a few years ago were unbelievable, no wonder why the army etc uses them lol.
I know alot of laptops cooling systems are under-rated and will do a good enough job quite often to see most laptops out of warranty and live for a while, but the XPS i have unless you kill it all the time in games runs at a decent temperature. Due to the ammount of hours its turned on, every 8-12 months i strip it down and clean the heatsinks, fans etc to keep it in good order. Dust in laptops is a major problem on every laptop ive ever seen and worked on, in particular if its turned on for many hours every day.