Never thought about the turning direction issue (it goes the same way as Sony/Minolta)...guess that would be a little weird!
The only times I see corner softness at all tends to be in the very open apertures at full wide - F3.5 to around 5.6 or so. ; Once I get to F8 and up, it's sharp all over on my copy. ; (The Sigma 10-20 I tested was ever so slightly better in corner softness at F4, but not as sharp on center - I tended to prefer the center sharpest...and since it was only wide open that the corner softness mattered, I tended towards the Tamron). ; All UWAs exhibit mild corner softness and distortion wide open - haven't seen a sample yet from the Tamron, Sigma, Tokina, Canon, Nikon, or Sony UWAs that doesn't have a wee bit of compromise in the corners at the widest aperture and focal range.
Getting close to subjects is very cool - almost freaky! ; You can just get impossibly close, where you think you're going to ram the glass into the subject. ; Definitely wouldn't want to walk around looking only through the viewfinder with a UWA on full wide - that whole 'objects in mirror are closer than they appear' effect would have you running into people!