I found the most difficult task was finding a high spec CPU with lots of memory in a laptop without having to pay for a high spec graphics card. I also demand a minimum build quality.
I am finding the main hardware problems that exist for Linux are related to power management and a BIOS that does not comply with standards.
I had to disable the power management scripts on my Clevo, otherwise I was finding my network card would fail if I wasn't connected to the mains power, and if I connected mains power while running on battery, the whole machine would freeze.
Power regressions within the Linux Kernel seems to be quite a hot topic of late, so it pays to be aware that running the newer Linux versions will reduce the battery life.
Other than the power management problem I am quite happy running Ubuntu 11.04 64-bit. The build quality is good and I have found it to be a good price point. It is a high spec machine running the i7 2820 with 16GB RAM. Cost about $2500AU with a , FHD 95% gamut screen and extra power pack. Battery life suffers a little due to the spec and PM problems, but I still get around 3 hours on battery.
In Australia the closest price I could find for the same spec and build quality at the time was about another $1000AU more. Apple had the physical build quality (feels sollid in the hands) and were one of a few that used the higher spec i7 CPU, but I didn't want to buy one since I had heard they had all sorts of issues with the new MacBook Pro overheating (the complaints thread was quite long as I recall and Apple were not officially recognising the problem at the time). Not sure if they ever fixed the problem?
Dell build quality I have found is quite good, my previous laptop was a DELL Inspiron 9400 and it has been running for the last 6 years and still works. My wife uses it at the moment for her studies. Unfortunately I would have had to buy the gaming machine version to get the CPU I wanted, ie around $4000AU, and again with a high spec GPU.
Looking around at all the current laptops, they mostly have crappy keyboards that flex. From my searching and trying in shops, only Clevo, DELL, Sony, high end HP (EliteBook) and Apple seems to have a decent keyboard. Once again it comes back to price, a good keyboard should not be exclusive to high end laptops, all laptops should have a descent keyboard without flex.
Then we come to the elusive good trackpad, Why do companies persist in making trackpads that have textures and sticky surfaces, the newer versions of Clevo also suffer from this from what I have read, using a rubber surface of all things? Luckily the earlier Clevo that I bought doesn't have the problems and its trackpad is not bad. Of course Apple wins hands down in this department, last I looked they have the best on the market.
If money was not an issue, I would buy the HP EliteBook as they have everything. Unfortunately they cost way too much in Australia, we are looking at a prices range of $4000 and above. The place I work uses the EliteBook range and build quality is great and I never hear of issues with heat, or noise. they also come with just about every port imaginable.
So hopefully this gives the op some idea of the problems in looking for a laptop in general and what I see as the mains issues when buying when it will be used with Linux.