Okay...I might have given it 4.5 stars if that was possible. But definitely more of a 5 than a 4. The only problem was that it didn't work perfectly at first in my 'test' site while I was upgrading from Joomla 1.5 to 1.7. I thought I was in for trouble. But I got a reply to my help request very quickly, telling me that it should work when I move my site from a subfolder and go live, and even gave me a fix if I wanted it to work under my test environment. (I was almost ready to go live so I didn't bother with that fix.)
Bingo...just as predicted, as soon as I took my upgraded site live, AjaxChat worked immediately...no other fix needed. It does what it advertises cleanly and efficiently.
Good product/good support. Can't ask for anything more.