I added a Seagate Momentus XT 750GB hybrid drive to my 2009 iMac to speed it up again AND gain some additional drive space. The iMac feels like new again. It's way faster than before. Since it took me some time to figure this all out, I thought I'd write a short blog post and leave a comment here, just in case there are others that are interested in doing the same. Let me know if you have questions. Pascal.