I finally found the comment problem: an obsolete version of the Javascript site template. Somehow I missed it during one of the (multiple) MT upgrades. Comments appear to be working properly now, which will no doubt thrill the two or three people who regularly visit here (hi, Mom!)
AH!
Now that comments are working again, I can leave a comment to tell you that comments weren’t working.
Outlook Web Access 2010 screenshots
Wanna know what OWA for Exchange 2010 looks like?
As always, Phil, your sense of humor shines through!