I've got one. It seems to do a pretty good job. I haven't noticed any serious problems with vignetting, going soft wide open, etc. The build quality is very nice. The hood is a joke. If you shoot with a 1.6x camera, I'd get the hood for the 24mm and use it.
If you plan on using it for panoramics, know that the nodal point at 17mm is very far forward. I'd swear that it's actually in front of the lens, if that's possible.