@MacTavish - I'm having exactly same experience on Windows 7. Somebody else on another thread pointed out the same thing you did - the menu/icon isn't visible... but it is running and working. Pressing "done" makes the icon go away - homeshare runs in the background.
It is a most confusing UI. Simply because you can see the icon in the list for a moment, then pressing "done" makes it go away which made me think "it crashed, where'd it go?!" - but turning on the AppleTV showed that it was working.
You have a Mac are are seeing the same thing us "PC" people are. Bug.. or intended functionality? No matter - it's Confusing!!
When my iPad syncs wifi with the PC I see it in the list, just like my old iPod (via USB). But there isn't any activity monitor for Home Share.
My AppleTV3 works fine. I can airplay to it from the PC, I can browse music/tv from the AppleTV, I can play from the iPad, home DJ works. Everything works. Just no "icon."
Windows 7, x64 Home edition (with every service pack and update available as of this week).
iTunes 10.6.1.7 (for Windows)
iPad 3, AppleTV 3 (slowly going apple ;-)