I've gotten the weird shading problems like in the image before, I even managed to get rid of them--but I can't remember how.  I'm pretty sure it involved increasing quality settings though.  Haven't got time for the next several days, but I'll see if I can reproduce what I did before on the weekend if no one else can help you out before then.  I've had problems with glass with this sort of thing, too.

Really, though, I'd just use a light with really soft buffer shadows for something like this, unless there's a reason you can't?