Well, don't get all excited yet - it wasn't a catastrophic failure.
... So, yeah, I still live. And I now have Mint on TWO computers! (Both a laptop and my main desktop monstrosity.)
I just now tried the APT-upgrade, and now my computer is... not right in the head. When I open Synaptic, it says something similar to 'APT::Default_Release: maya not a possible release name' - I don't remember the exact message, but it looks like some LSB, or deep seeded APT file wasn't updated correctly. (GRUB also shows the wrong release names, though both lsb-release and issue/issue.net show the correct information. Is this relevant?) And, well, with that, Synaptic tells me to smurf myself and dies. I also don't seem to have an internet connection, but I haven't looked into that - it's possible a kernel add-on takes care of it, as it has in the past, or some firmware... But besides that, I have no problem whatsoever - YAY! Uh, help?
I should probably also say that the upgrade didn't go completely without a hitch - some kernel pollution (installed the lts-quantal version prior to the upgrade, the new kernel package went bonkers) though a subsequent dpkg install -f proceeded with no apparent problem...
What can I say, I'm not big on burning DVDs left, right and centre, and I like my USB stick the way it is, thank you very much. (Yes, yes, burning the image onto it is definitely something I can do - I've managed to keep an Arch-installation going for a month, most of the time even behaving the way I wanted it to; I simply prefer the APT method, so I don't have to run around picking out my packages and PPAs YET ONE MORE TIME.) I'm not dogmatic against the idea of using a proper installation DVD/image, I promise.