New glass is fun...600mm will give you quite a bit of reach for wildlife (hopefully it isn't a beast to travel with and handle).
I've been surprised how close you still need to get for good wildlife shots, even with a long lens...plan on getting close enough to smell those bears. SMELL THE BEARS!
Yeah, it isn't exactly small. I think it weighs about 4.5 pounds, and the filter size is 95 mm, so you can get an idea how big the sucker is. Monopod and ball mount is a necessity for extended use. I found a backpack bag that can hold the lens and 3-4 others, so I think I'm all set. I might have to get some bear repellant.
Here is a picture of a Japanese lady holding it at the Sigma booth at a photo gear product showing.