I also have a G2 and use the Ikelite housing. I have been extremely happy with the housing and my newly aquired Ikelite 125 strobe and TTL sensor.
Although I plan to write a more extensive review in the future, after a dozen dives with my Ike housing and G2, I can only say that it keeps the camera dry, it is easy to install and remove the camera, and that all of the controls function correctly.
My only complaint is the somewhat funky design of the external flash blocker, it is far from elegant!
I would also definitely consider a camera capable of using a wired strobe if I were starting from scratch to purchase a digital underwater photo system. Since I already owned a couple of G2s (I generally like the image quality) I did not have this as an option.
I would purchase another Ikelite housing in the future if I decide to go with a dslr or a different compact digicam. Ikelite provides great customer service and stands by their products.
click on the link below to see photos from my first dive with the G2. These were taken with the internal strobe.