I started my quest for a lighter pack in early 2006 (my old external frame, which I hated, was 5 lbs) by going to REI and trying on most of the packs in the store. I didn't find one I liked because every one was too heavy--they had nothing that weighed less than 3 1/2 lbs! However, I did get an idea of how a comfortable and well-fitting pack should feel. A wasted effort for REI, but not for me!
I resigned myself to having to order half a dozen cottage manufacturer packs and probably send them back. After much research, my #1 choice was the "Comet" (since discontinued) from Six Moon Designs. At the time I decided to order, the 2005 model was on closeout sale since they were changing the fabric and design. I didn't have time to drive across town to Beaverton (I live east of Portland), so I ordered the pack online. As soon as it arrived, I packed in my gear, the equivalent in weight and bulk of a week's food and 2 quarts of water to be sure everything would fit. I then adjusted the pack and hiked around the house (it was raining outdoors) for a couple of hours. Most boring hike I've ever done, but it was worth it to be sure the pack would work for me. Fortunately, the pack fitted as though it had been custom made just for me! I'm still using this pack 6 years later, and it still works great and is holding up just fine.
Of course not everyone will be that lucky ordering online, but advance research really helps. You are not going to find at REI a 27 oz. pack with stays, a good hipbelt and load lifters that will carry up to 35 lbs. in a pinch. If you want a lightweight pack, the internet is it, and you have to be prepared to pay some return shipping.
PS: If you're going to start at REI, wait until several weeks after the current 20% off coupon expires (April 15) and they've had time to restock. I went in early April (the coupon expired the end of March that year), and their stock was pretty thin!