I just got my 24" 2.8Ghz iMac, and I can't say enough good things about it. My first Mac in a while, and I am impressed with its performance. I was using a Quad Core 2.66, 8GB Ram, Nvidea 8800GT w/Vista 64 bit as my main PC, but decided to make the switch since these refurbs came up at such good prices. I haven't noticed any drops in performance going from the Quad Core 2.66 to the Core 2 Duo 2.8Ghz - and this iMac actually feels faster (mostly to do with OS X vs Vista I would imagine).
Unless you really
need a better performing GPU, I think the ATI 2600 does a pretty good job. I don't game on my computers for the most part - but I bought my kids a Wall-E game that happened to run both on the Mac and Windows. I had the game set to full resolution and it seemed to be very smooth and play very nicely.
There is a review around here that benchmarked the new 2009 iMacs and had the 2008 2.8 Ghz w/ ATI 2600 in there as a comparison. The 2.8Ghz w/ ATI 2600 blew away the 2009 iMacs with the Nvidea 9400m by a wide margin.
If I was looking to spend more and get a 2009, the only way to get a better performing iMac is to step up to the 2.93Ghz with the GT120 for $1799, which for me was just not worth it.
I disagree with what Lordsion had read about it being slow. It is actually one of the faster consumer 'Desktops' that Apple makes. Here is the benchmark review from Geekbench (they haven't updated it with the scores for the 2009 iMacs yet):
http://www.primatelabs.ca/blog/2009/01/mac-performance-january-2009/#consumer_desktop
In my opinion the 2.8Ghz refurb you are looking at is one of the best deals going in Macs right now...
