In reply to markez:
Yeh, I've gone off floating lids a bit. They rarely form a weatherproof seal, so if you're climbing in wet conditions they can let moisture in the top. And when empty, they often sag and flop around - depends on the design.
Also, the extension is really best for voluminous but light items like down jackets, as if you load up these packs so far above their basic geometry they don't carry as well. If you're regularly using the lid extended you should just buy a bigger pack.