I have to add my voice to the chorus of approval for this lens. I've had it a few months, and it's been great. The price was so low (~£350 I think), that I felt able to take a gamble, and it paid off (I was heartened by the consistently good reviews I found online).
It is solid, and I dropped mine (don't ask!) a few feet onto a concrete floor, and it survived with no more than scuffs - the built-in hood does seem to protect the bulging front element. It has next to no fringing, as the reviewer said, and the sharpness is great.
A few gripes: when mounting/removing the lens, it's pretty much impossible not to twist the aperture ring, so it's hard to keep set (although easy to put back). On my copy at least, the distance scale seems wildly inaccurate - for astrophotography, I find 0.7m the right setting for stars - and anything closer to infinity is out of focus. Flare is often present, even from relatively minor light sources, but it's often unobtrusive. And of course, the inevitable lack of exif means you can easily forget precisely what aperture you were using.
But these are minor, and I wouldn't hesitate to recommend this lens to anyone looking for an ultrawide, unless money was no object. I have a small Flickr set of images taken with this lens here: http://www.flickr.com/photos/scyrene/sets/72157636579799955/
, and I'll include a couple of images below to give an idea.
One last note, it is very challenging to get good composition with this lens, but that's down to the focal length. I'd never shot wider than 24mm on full frame, so it was a shock (even having seen lots of other images). It's very tough getting symmetry and a level horizon, and when you adjust for distortions, this can be a problem. But it can yield fantastic results when things go right.