I do not know how anyone uses the thumb buttons. perhaps that is a weakness of the G5/G7 models, but I feel the thumb button requires excessive pressure, and does not feel like a natural button position at all. The pressure required to activate it actually prevents me from being able to precisely and smoothly move the mouse around and fire while pressing it. If you feel the thumb button is very important for some reason, I would not choose the G7 without first trying it yourself.
However, the only thing I could see that being useful for is vent, teamspeak, etc, and those are also easily accomplished via a keyboard key.
I do not understand the above comment that the G7 is only good for gaming, and not for web browsing/photoshop? gaming is the most demanding and precise requirement for a mouse, how would it not meet the requirements for something else? hopefully the person will clarify on that.