I've had this lens for a long time, thought about selling it a few times, but still have it. It's seen service on an F100, D300, and now a D800.
Fact is, I'm not really an ultra-wide sort, so for occasional use this lens is great. It's main advantages are it's inexpensive (or, at least it was when I bought it, and I presume it still is on the used market), very lightweight with great color and center sharpness (really, most of the frame is pretty darn good).
Yes, there's plenty of distortion which can't be corrected on film, but trees are crooked, anyway, and unless I'm shooting over open water, so's the horizon (ever heard of hills? ), so the distortion never bothered me. And with the fantastic resolution of the D800, I have no qualms about using LR4's lens correction settings.
As others have noted, the corners never really sharpen up on FX, but that may not be a problem depending on what you plan to shoot. For my uses, it's a keeper, but if I were buying new today I'd probably check out its successor, the 16-35VR, or the 3rd party offerings which may not be any more expensive than a used 18-35 and may have better corrections for digital sensors (the operative word being "may").