I've had my G9 for a while now and I find it very comfortable. I work from home and do a lot of gaming so I'm on my computer something like 16+ hours a day.
If you like larger mice though, you probably won't like the G9. It is rather short.
I'm very happy with it though. Definitely the best mouse I've owned. (to be fair though, I've only ever had two different mice - a MS Intellimouse and a Razer Diamondback)