Besides making the most excellent Macquariums, when I was in college I saw Mac Pluses being used in the computer lab as quickie email stations. Since that model had the ability to boot off of an OS that was embedded in the silicon (instead of the traditional boot floppy), it was a cheap and easy email station. Plus the administrators didn't have to worry about viruses.
I'm not exactly sure what you're talking about when you say "boot off an OS that was embedded in the silicon," but as far as I know, the Mac Classic is the only compact Mac (in fact, the only Mac) that has an OS in ROM. In fact, it's Mac OS 6, and you can get to it (if I recall correctly) by holding down Command-X-O at boot time. It's a cool unit thanks to that feature, otherwise it was extremely underpowered and overpriced for the time it was released. You are probably thinking of Mac Classics.
However, the Mac Plus is cool because you can do quite a bit while booting off one 800k floppy. They have no fans, so the only noise you'll ever hear is the occasional floppy drive read/write, and the banging of your head against the table when you lose in Hangman.
(As an aside, the school also had stand-alone PC email kiosks. The IT folks tried locking them down as much as they could - removed the MS-DOS prompt from Windows, hid everything, etc. But the smart nerds just emailed themselves copies of the MS-DOS prompt program (this was Win 98, I believe) and through that they managed to have some very good Warcraft and Starcraft LAN matches on those things :twisted: )
Heh.. try as you might, Win98 just can't be locked down. Thank Microsoft for one of the worst OSes ever created.