SAV 8.1 currently seems to be using around 13MB of RAM and 16.4MB of hard drive space on my laptop (this includes realtime file protection as well as the automatic definitions update service)
As far as I can see, it supports Lotus Notes and Microsoft Exchange, in addition to file system realtime protection. Not quite sure about Eudora compatibility.
Symantec, of course, releases new definitions every weekday in the form of the Intelligent Updater (IU), so it's effective in detecting new viruses. It's a well-known fact, though, that the unpacker of Norton/Symantec isn't too great, so it fails to detect some packed viruses and worms. I know Kaspersky (which is quite resource-heavy AFAIK) can detect those, but I've never used AVG, so I don't know about that.
All-in-all, however, SAV 8.1 is a great AV, and I've been using it for quite a while now.
I'm moving this thread to the Security section so that you can get more feedback from some of the pros.