I just got this lens a week ago. It was $700 used. After thoroughly testing it out, I am a happy camper. I agree completely with mannetti21's review. The only practical issue I had with the lens was a slight bit of struggling to focus in very poor lighting (f/2.8, 1/60, 6400). Most equipment struggles in that kind of light.
The vignetting at 70mm is relatively huge, at 2+ EC, but is only visible at f/2.8. By f/4 it is not noticeable. The LR profile cleans it up very nicely, but you have to shoot raw to use it. It is not standard, smooth drop-off vignetting. On this lens it is pushed WAY into the corners, and drops off very fast. That makes it very noticeable, and hard to correct manually.
The distortion at 24mm is heavy. It is gone by 35mm. Again, the LR profile cleans this up beautifully. Because of the wide open vignetting (worse at 24mm & 70mm), and the distortion (only a factor at 24-28mm), I shoot this lens raw, so I can correct both when necessary.
In processing, I find this lens needs a touch more added contrast than usual. That may be because I push ETTR all the time, and I shoot this lens raw (N, 0, -1, -1, 0). That said, I am completely happy with the results this lens produces.