When I am shooting video or packing my camera on the stream — my pack of choice is the Fishpond Shooting Star backpack with a small drybag in it that I keep open (think of this as a simple inner liner for the bag with the added ability to roll it closed if it pours) and inside that I keep a Lowepro Toploader 75 which will hold my D70 w/ 80-200 ED attached to it.
I’ve had my Mountainsmith for years (got the idea off of Sportsshooter, been a member for years) and it’s good for covering football and such, but not really for streamside work. I’ve actually stopped using the MS pack two years ago when the newspaper bought me a ThiinkTank waist bag.
For anyone looking for bags to transport your gear between shoots, waist bags (fanny packs) or a modular belt system, take a look at ThinkTank.com.