17-55 F2.8 came yesterday. I only had a few hours to play around with it (basically indoors, under less-than-ideal lightning conditions).
My initial impressions are somewhat mixed: build quality is OK I guess, definitely not "great" (lots of plastic, little bit of play on the focus ring, even more play on the zoom ring).
Usability: heavy as f/ck, this helps with the micro-shakes though (also, the IS feels to be a tad better than the kit lenses IS).
F2.8 - as indicated earlier - is not a world apart from the 3.5 on the kit lens, under these lightning conditions both need noise reduction in post, which is a pity. Of course there is a LOT more noise with the kit lens, but after NR there is very little difference. Of course less noise also means better utilization of the available bandwith for the codec, but it's a 10% difference, not a 30%.
Sharpness: need to test with some ISO charts I have printed, but in practice the difference in sharpness is only visible when looked at at 1:1 on a computer screen: pretty much identical when it comes to video.
AF is again a bit better than the kit lens, but in low light it hunts too. Ultrasonic motor is a bit better (faster, more quiet) than the regular micro-motor on the kit lens, but it makes too little difference.
At this point I am trying to come up with a good reason why not send it back and so far I have not found one. Maybe my expectations were a bit unrealistic, or I got a lemon (or a very good copy of the kit lens who knows).
