I'm kind of disappointed - some of my VMU's memory became corrupt. I don't know why...
I first realized something was wrong when my Sonic Adventure file was missing. When I went to check the VMU in the Dreamcast's explorer, there were only four files there - my Skies of Arcadia save (thank goodness), my Guilty Gear X save, and my Power Stone 1 & 2 saves. I checked through my other cards - Sonic wasn't there, either. Also, between those four saves, only 49 blocks should have been occupied on the card. However, the Dreamcast reported 3 blocks free, which would have brought the total to 52 blocks... and a normally-formatted DC memory card should be 200 blocks...
So, I moved the remaining files over to another card and reformatted the faulty VMU. It seems to work fine now (although it looks to me like the little notepad icon on the VMU is lit up...). I'm also storing it further away from the TV screen, as I know there's always the possibility of EM interference messing with the stored data.
So, now I have to play through Sonic Adventure again. It shouldn't be the end of the world, as it's a good game... besides, I never did beat it. I got stuck at one point and couldn't figure out how to continue. I'm unhappy that I lost my records, though. I don't know what else may have gotten lost on that memory card, but looking through my games and the saves I have stored on other memory cards, it looks like most of the saves I care about are backed up in one place or another.
On the bright side, I already knew that the original Soul Calibur was awesome... but I didn't realize HOW awesome until today. Added bonus; it was one of the save files that didn't get lost. I love the little character animations on the VMU, and the animations, art, and extras in-game are fantastic. Such a great game. I finally had to call it quits, because I was getting tired and my thumb was hurting. If neither of those things had been a problem, I'd have kept going. I want to unlock everything.

I have my Saturns, I have some of my games, I have a RasPi. Gotta put all this stuff together!