Il Mio Problema
The 2008 iMac with 4 gb RAM runs Yosemite, but just barely. You spend lots of time watching the beach ball spin, and the video is glitchy. It needs more RAM! Apple says the machine only handles 4 gb, but you guys said take it to 6 gb.
La Mia Riparazione
RAM installation is easy with this machine- it's finding the correct 4gb memory card that is hard. ifixit is the only place I found that had the right card.
Il Mio Consiglio
Do this upgrade! My 2008 iMac now runs Yosemite like a champ, including my 100 gb Photos library. $100 is pretty cheap to make my machine feel like a new $1100 iMac!