In reply to Denni:
I've tried one on in Needlesports. The chest pockets are fine and won't interfere with a strap, but something as heavy as a modern smartphone deforms the shape.
I think the Nano Air is more akin to the Rab Strata than the LT. The LT doesn't breathe as well as the Strata (I have the Rab, my wife the LT). The main differences are:
a) stretch, the Strata has some but the Nano Air really strrreeetttccches
b) 2-way permeability. The Strata (and other polartech alpha pieces) is basically windproof, the nano air is not. This matters because on the one hand it allows for more cooling on the move (good) but requires you to throw on a shell (wind-or hard-) when resting for prolonged periods in the windy UK (bad). This latter weakness makes a nonsense of the claim that this garment does away with frequent costume changes. Patagonia puts a better spin on this weakness by stating that " pull a lightweight shell on over the Nano-Airâ„¢ and it's thermal properties skyrocket!" So you still have to throw off your pack and put on a shell. You won't need to do this with the Strata or LT until conditions are somewhat more severe, but you'll cook faster on the move.
All in all I liked it. Super lightweight and very comfortable but cut rather baggy for the typical Patagonia prop forward cum rock climber. I'd like to try one in the field (=own one) but between my ME Eclipse microfleece and a Rab Strata I'm not sure if the niche is big enough.