One of the cool things about it (and this is not really about Memtest, even though it factors into it) is that there exists a Linux kernel patch that makes it reliably use bad memory by avoiding the bad spots. Oftentimes, memory goes bad in such a way as to cause only particular offsets to fail, and you can use Memtest to find those bad spots and produce the correct configuration information to then tell Linux to not use those areas of memory. And it's a pretty slick solution, too; it just allocates those areas of memory in the kernel as if they were being used as data and then never uses or releases them.

Anyway, not really about Memtest, but it talks about it in the Memtest config, so I get reminded every time it's brought up.