Yourlensreview - Lens - Canon EF-S 17-85 F/4-5.6 USM

The IS is very useful in the situations where you can't or selectively use your flash. The range is also extremely useful. Wide-angle (also on a 30D) and slighly going to tele.
The lens ways almost nothing, so it isn't a burdon on my wrist when I'm on a party-shoot.

Build quality. My lens has a lot more wiggle-space when I put it on 85mm compared to the moment I bought it. I think this is to much, but I havent noticed any performance-loss.
The extra space the IS uses (the extra hump on the lens with the controls on it for IS) can move nowdays :-S It's a few mm's, but enough to notice.
On 17mm it's beginning to fish a little bit. Not noticable when no straight lines are to be seen from left to right.

For a Canon lens of about € 675,- I hoped for a bit more build-quality. Apart from that the lens works fine. I bought it because te Sigma 24-70 F2.8 gave me to often a hard time when I wanted to take partypics of people in groups.

If you want a good all-round lens to start with, I would recommend this one. It can save a few pics in darker places because of the IS. To be honest; it's my default lens on the camera. And I took about 30.000 pics with it and still love the bugger :-P

Extremely useful range for a standardzoom.
Image stabilizer very useful for low light handholding and 'dragging the shutter' flash photography.
Very fast accurate autofocus.
Acceptably sharp centres wide open.
Good vivid colour and contrast.

CA and Barrel distortion.
Extreme borders on the soft side.
Zoom tends to be 'sticky' when trying small adjustments.
Typical narrow EF-S USM focus ring.

Despite the optical flaws, I still think this lens was the right buy for me when I bought it.
No other lens packed Ring USM autofocus, very acceptable performance, Image stabilizer and above all a very very versatile range in one lens. These days there is comptition from the (much) more expensive Canon 17-55/2.8 and 24-105/4 lenses thought.
Unlike with some other popular lenses, the flaws this lens has on the wide end are fixable in post-processing to an extremely good level, just in case the problems appear objectionally in the final result.