I'm running a very similiar system to everyone else except a few differences:
I'm running XP Pro, not Vista. I have the driver installed that essentially disabled the Intel Turbo Memory. I'm running the X3100 integrated card rather than the nVidia GPU. All drivers are updated to the latest drivers as released on the Lenovo downloads page for the T61 series. Everything else is nearly the same in terms of problems with the BSOD.
I purchased the laptop back in January and received it in February. I posted this in a seperate topic because of the problem has only been specified as a VISTA ONLY problem and I have seen no topics on the same situation on XP. I just thought I would point this out to make sure this wasn't thought of as a Vista only problem. The BSOD only occurs when dealing with anything that is graphic intensive; games, 3dmark, etc.
So the question becomes, is this a motherboard problem or a driver compatibility problem? From what I've read so far, it sounds like it's a hardware issue with the DIMM slots themselves if Lenovo is swapping the mobo and the problem is disapearring. I don't feel like bumping upto 4gb and switching back to Vista if the problem is still happening on that OS as well.