I own my third Giro G10.
I am on my 3rd because i fall hard a lot! It is a little insurance that it will still be good when I need it. Also I can sell the year old one and get a new one, for around $10-$15
The G10 has very good venting, and is controllable by a switch like Andy's Fuse, but they are different head shapes. My current one is the MX model, and has a visor on it. The main reason I like it is that when bashing through the woods I just lower my head when there are branches, and it protects my face. I can hear very good with the soft ear pads.
I also own a Giro Talon for racing.
It provides more protection and is race legal(I was going to be racing in college).
It is not nearly as comfortable as my G10, and I can not hear as well. I would only recommend a full helmet if you are racing.