on my 5d ii
How is the lens?
I use this lens on my 5d ii and have been quite happy with it for outside photographs.  I am a professional photographer and I love the 24-105 zoom -- it allows me to get environmental portraits -- i.e., a couple in front of a church or a small child on a beach -- and then I can zoom in for a more traditional portrait (the bokeh is quite nice at f4 105).  I find this zoom range essential for event photography.Indoors I am not quite as happy with this lens -- I have to ramp up my ISO pretty high as I am rarely on a tripod indoors (weddings and events).  If this lens came out in a 2.8 I would replace it in a heart beat, but I am not interested in the 24-70 2.8 because I would miss that extra focal length.Anyway, this is a great all around lens and is my favorite for event photography and as my personal "walkabout" lens when I'm on vacation.  Not too heavy, very versatile, and it takes excellent photographs.update:  Indoors with a studio setup, this lens is also FANTASTIC and is on my camera 80% of the time.  Because of focal length focusing issues, I can't use my 70-200, but I can get pretty close to my subjects and fill up the frame with the 24-105. 