All of us in the NZAT were stoked to partner with Julbo NZ recently, and as a result of that partnership we've each been given a pair of Julbo's latest sunnies to try out. Personally, I chose the Shield glasses, which have Julbo's top-of-the-line Chameleon lenses - polarised, antifogging and photochromic ('cat. 2' to 'cat. 4'). I can quite confidently say (in my therefore completely objective opinion) that they are, hands-down, the best sunnies I've ever worn.
First off, the photochromic thing is pretty cool. It's just like those 'transitions' prescription glasses some people have - they literally change their light transmission properties depending on the amount of light (cat. 2 lenses are for normal daylight, cat. 4 is for full-on sun on a glacier). Your eyes get about the same amount of light coming in even as the strength of the sun changes.
For years, being a cheap student, I've been wearing some basic old Julbo glasses that I found one day in an army surplus store. I don't even know what model they were. The shop had a bunch that were lightly used, and going for $25 a pair, so I bought four pairs, which I've just utterly thrashed over the past 6 years or so (~1-2 years of life each). I used them at altitude in Peru, ice climbing in Canada, mountaineering in NZ, and they did the job. But, they were full-on cat. 4 (i.e. for the harshest sun) and frankly they were too dark most of the time. In whiteout conditions they weren't much help - you need something on to protect your eyes from all the UV, but they were so dark I could never make out any detail in front of me (and in whiteout conditions, on snow, being able to see ANY detail in the ground is the difference between being able to carry on moving, or not). The Shields on the other hand are just right, all the time. I'm actually not sure how I'll put up with non-photochromic lenses again.
I'm also loving the polarisation and colour tint of the glasses. They are a slight rosy shade that brings out colour and vibrance in the surroundings without seeming artificial. Friends who try them make approving noises about how good things look through them - that's got to be a good sign. The lenses are crystal clear and you can see detail perfectly. The antifogging seems to work perfectly (I've used them running), and the lenses don't seem to attract dripping sweat quite like my last glasses did. In particular, I've used the Shields lots over the summer doing botanical field work, where you're out in the full sun and need to be able to spot tiny individual plants amongst the rocks and tussock - and the Shields have such good clarity that I can spot the tiniest leaf from some hidden plant just as easily as wearing no sunnies. Not so my old pair of sunglasses, which turned each leaf into pretty much the same dark shade as any other leaf (some readers may have this problem generally with telling very small plants apart, but I can assure you that there are differences).
My only concerns with the the Julbo range is with fit - I have a narrow face and also have trouble finding narrow enough prescription glasses (I seem to generally suit ~size 50 lenses, which is right at the smallest end of what you can normally find in the mens' prescription glasses). Others in Julbo's mountaineering range, like the Explorer 2.0, were way too big for me. I guess I could try the women's glasses and hope no-one notices (they are pretty hot after all). Instead I went with the Shields, which fit a bit smaller than the Explorers. I've put some elastic in the convenient cord attachment holes (just in case), and they don't drift down the nose much at all.
So, although the Shields are bigger than what I normally choose, they actually fit me pretty well (I can't comment on whether or not they suit me - haha). They have never fallen off yet and I've been using them in the mountains, rock climbing, running, tramping, fishing and working. I'd have liked a more adjustable frame (like the classic rubber-coated wire on Julbo's older-style mountain glasses) to really make them perfect. For now they're pretty close.