I haven't had any problems with my new 15" PB (2 GB RAM, 7200 rpm HD) except for brief period of screen flickering right after I'd downloaded and installed 10.4.3. That seemed to be a temporary situation, no reoccurrances later. No lines, no faulty case closure, everything looks and works the way it is supposed to. I ordered it BTO from the Apple online store, as my local Apple store didn't have the machines with the 7200 rpm HD in stock yet and didn't have the RAM that these new PBs take. Although I have installed RAM in computers in the past, knowing that Macs are a little fussy about the RAM used in them, rather than ordering from a 3rd party vendor and putting the chips in myself, I decided to just let Apple do the RAM even if it did cost me a bit more money. I'm fortunate that I haven't experienced any of the issues others have discussed on here -- I guess it's the luck of the draw....
As for the potential heat issues, I haven't noticed mine getting excessively warm, but as a precaution I did get a thingy called the iLap (ordered online from raindesigninc.com), which is meant for PBs and is aluminum, too, raising the laptop up a bit so that there is plenty of air circulation under it. It comes with a detachable velvet cushion thingy so that one can use it either on your lap (with the cushiony wrist rest) or on a table/workstation/desk surface without the cushion. It really works well. Yesterday I had my PB running for about ten hours straight as I was transferring files from my old PC into it and at the end of that time it did not feel excessively warm at all. Just my experience...
OTB