If you've upgraded your early 2008 iMac from Mavericks to Yosemite, post your experiences here, along with how much RAM you're running. I'm wondering whether there's a performance hit.
It runs very nicely on the few test machines of that model I've put it on to. Most have 4GB of memory, a few have 2GB. All run it well with little difference from 10.9.
I've loaded it onto a 2009 (look at my signature for specs). It has been running perfectly. The only thing I might have noticed is slower boot and slower changing accounts. Seems to take a little longer time (get the spinning timer, clock, whatever that thing is) after putting in the password and then the desktop appearing.