This is pretty much the perfect pack for those who are considering buying it (not for the average backpack user). I have used it extensively while mountaineering, ranging from winter mountaineering to the Himalaya. It performs very well, with things pared to the bare minimum, but no less. Even when filled to the gills the load stays out of the way.
Quibbles: the kangaroo pouch isn't very durable, I've put a fair number of little holes in it over the past 2 years. That being said, the rest of the pack is bombproof. Also, a sternum stram would be nice, just to keep the shoulder straps well behaved while 5th class climbing (they have simple straight foam padding inside so they tend to want to go in odd places).
Now if only it came in smaller sizes...

I just got it, had it out 3x but LOVE IT so far! Light as a feather with plenty of room. Rarely needed the hipbelt on a 5 day trek on the Tuscarora Trail. Helped me get my week-long backpacking load down to <30#, and that's for 25 degree weather, give or take. Not for those who like pockets, you have to think before you pack, but it'll hold all my climbing gear, once I'm done GETTING all my climbing gear...

GoLite Gust pack, how do I love thee? Let me count the ways ...
-One .. you're so light, but you fit so much stuff.
-Two ... You don't mess around with a bunch of extra bells and whistles that I don't need
-Three ... Your webbing hip strap is nice to have around, but you're so light that I rarely use it.
-Four .. the features that you do have - tool loops, front pocket, drawstring top - are all very useful and right where I want them
-Five ... you're priced well! I can afford you!
Six ... see number one.
[b]Cons:[/b]
-Not for folks who want to carry more than 20-25 lbs. I usually only carry 12-18 or so.
[b]Value:[/b] A+ ... great gear, great price