Well, I took the plunge and installed it. Seems to be fine so far.

Desktop Environments plug into the X Server and are largely unrelated to the kernel. It's not like the X Server is the Shell like the Windows equivalent either. It's just a program that enables a GUI environment, if you want one.

The most likely issue to arise when messing with desktop environment packages, assuming the distro does its job, is breaking the library dependency chains and thus blame can be pointed at the automatic package handler. If the distro's package handling program isn't pathetic they should be able to do a repair such things easily by switching to a terminal and using the package manager utility, and thus he didn't "have to" reformat anything. Even if it was the kernel either his distro should have done the usual backup the old kernel or he should have done it manually, given Linux is specifically designed to allow you to run multiple custom kernels for various things, if you want to, in addition to most distros in Mint's category automatically backing up the kernel when they do a changeover.

Really though you're pointing at Debian Unstable repackaged twice, by groups that release lots of patches release day +1, like it's supposed to be a stable distro. So you can pointlessly "insult" someone who bought Windows 7 and is having problems. And do note that distros like Mint make a business of modifying perfectly good apps/kernels as fits their specific biases, and thus are not representative of vanilla unlike Slackware and similar. Blaiming anything that's their fault is like blaming Microsoft for *insert third party app that's supposed to improve performance* messing up your system.

A Blue Screen of Death is more accurately termed a Stop Error is equivalent to a Kernel Panic, which you almost never see in Linux because one can rather safely say the Linux Kernel is the most debugged Kernel in existence (see Linus' Law). Instead Linux issues usually revolve around dependencies as related to packages caused by automatic package handlers doing something they shouldn't. Just like your roommates issue. Implying a Kernel Panic or most other Stop Error issues have nothing to do with the OS, because in Windows it is often driver related, with a system that was apparently stable prior to the SP1 upgrade is simply put, stupid. Particularly as Microsoft not only provides a kit to make drivers, but certifies them given we are talking 7.

Given Service Pack 1 clearly is modifying the Win 7 NT kernel, unintended issues related to the kernel before Microsoft is effectively suggesting you pull the trigger isn't exactly a novel or radical concept. Note the kernel is the OS at the most fundamental level possible so saying it's not is Orwellian in the extreme. Now you could have said something about Kernel instability being exaggerated with Windows or that best practices argue for a degree of caution when doing kernel swaps, but you didn't.

Slackware, which uses a vanilla kernel and apps, and avoids automatic package handling problems is extremely stable in any sense of the word, and RHEL is rated well above Windows for stability. Seems as how Linux refers to the kernel, GNU refers to the community developing the vanilla utilities, and distros tweaking things is downstream of that your statement makes zero sense. At most you can refer to the distro family or the problems of using automatic package handling.

FOSS drivers can be mended by the end user themselves and are often subject to Linus' Law thus preventing the issues in the first place. Particularly as a lot of kernel updating revolves around adding and stabilizing drivers. Proprietary Windows drivers on the other hand are as a rule utterly close source, as is the Windows kernel and shell. Hence the driver maker is operating blind and you can't do a lot about breaks when they do occur, unlike Linux.

Word of warning Direct2Drive's Comrade client doesn't seem to like SP1 in fact every time I try to start it it gives the usual "Comrade has stopped working" message. Gamespy who run the shitty thing claim to be on the case which probably means they are waiting to get a new work experience kid to do the coding. In the meantime if you are a D2D customer then don't upgrade to SP1.