The addition of the 8800GS brings an enthusiast GPU to the iMac line. I couldn't find any quick benchmarks online for this card but it does seem to be slower than the 8800GT spec wise. However, it should be more than good enough for some moderate to heavy gaming. Yes, I do know that gaming has never been a strong suit for Macintosh. However, there are some big name games coming out for the platform so Mac users are not left high and dry. Also keep in mind that you can run Windows XP through Boot Camp and play all your favourite Windows games on your iMac. 

Another thing worth noting is that these new systems don't seem to use the Merom core anymore in their CPUs. There is a possibility that the 2.66ghz model could be a Wolfdale though it's more likely the older Conroe E6700. Since Conroe uses a different socket than Merom, we can assume these are Socket 775 motherboards. The 2.4ghz is probably an E6600. The 3.06ghz model is interesting because there are no stock, off the shelf Intel Core 2 processors that run at that speed. Of course I could be wrong about all of that and they could indeed by custom clocked Merom or Wolfdale CPUs. This thing is badly wanting to be ripped apart to see what its guts are.

The iMac with the 8800GS and 3.06ghz processor is a whopping $2199, which is expensive for what it is. The two 20'' models cost $1199 and $1499 respectively while the lower end 24'' is $1799. If you want to consider buying one of these, I'd stick with the two 20'' models since these high end ones are overpriced. If you want a gaming system, you could probably get a similar PC system with a vastly superior GPU for the same cost. For a decent office or multimedia system, the 20'' models are perfect.