Well, I finally seem to have solved the the problem I was having with my Thinkpad(s). (Summary: BSODs, intermittent freezing, strange start-up problems -- with both a Thinkpad T41p and a brand-new Thinkpad T42).
After years of being totally fed up with system freezes once every day or two, I decided over Thanksgiving (in desperation) to replace all of my memory with RAM purchased directly from Lenovo. Since the moment I put the new sticks in, my machine has been running *absolutely perfectly* (during testing, I left the machine on for a few days (in constant use), and also taxed the CPU, disk, memory, and network interface for 8-10 hours at a time, overnight).
Previously, all of the RAM in the system had been purchased from Data Memory Systems, from whom I have been buying RAM for years and years now. All of the desktop RAM I've purchased from them has worked without any problems (my desktops always stay up for months at a time with no crashes), but nearly every time I've purchased RAM from them for any notebook (specifically, Dell and IBM notebooks), I've had problems. In my experience, not a single notebook with DMS RAM has run stable enough for my standards (which means that they shouldn't really ever crash, other than perhaps the very occasional BSOD that comes along with being a Windows user ;).
I've also probably exchanged 50% of the sticks of notebook RAM I've purchased through DMS, even though those same sticks had passed memory testing with programs like MemTest86+. And when I sent my system in for service (warranty service through American Express -- again, I was desperate), the tech guys claimed that everything passed tests just fine.
I believed them, but the problem was that despite passing tests designed to stress specific pieces of the hardware, my machine -- even with a near-virgin install of Windows XP -- was still freezing frequently, with no apparent pattern or cause (it would freeze while playing movies, web browsing, moving the mouse, and even while just sitting there without interaction).
Normally, I would trust the professionals whose job is to figure out why a machine is not working, but in this case there were so many similar reports of Thinkpads freezing -- and not starting back up -- that I knew that the problem had to be a hardware issue.
*UPDATE 12/30/05* My machine hasn't crashed once since installing the new RAM. It's so nice to again have a machine I feel I can rely on!
Anyway, as a result of all of this wasted time, I've decided that for notebooks, I'm sticking to manufacturer RAM (or perhaps memory from Crucial, which they claim to actually test with specific systems). The $150 (or whatever) that I would save from buying cheap RAM just isn't worth the hours and hours of associated headaches. It's strange that my desktop experience has been so different.
I hope my current notebook stability continues...