Well, I gave it the old college try, but I ended up pretty well trashing my site in the course of my attempt to upgrade to Subtext 2.0, so I had to get restored from backup. Yow!
There seemed to be something odd to begin with when the upgrade process wouldn't run - it sort of locked me out of the site. I got around that only to see it say I needed to "install," not "upgrade." Ummm... well, OK. So I did that. The database got upgraded, but then I hit the final wall: I'm in a medium trust environment and the build won't run in medium trust.
Looks like I'm not the only one having a problem.
I guess I'll have to see if I can help rectify some of this.