24 II corners are pretty much like the 24-70 II and much better than on the 24-105 or 24 2.8 non-IS. Of course a 24 2.8 II non-IS could cost a lot less than the 24 1.4 II and weigh less and be even better.
I wonder how the 24 2.8 IS performs.
Ask and ye shall receive:
Do the mouseover and watch the arrow to show what is being shown at the time. I've compared to the gold standard 24mm T/S II, starting at F/8 but you can change that as you need to. I think the new 24 IS solid in the center but leaves something to be desired in the corners. The T/S really seems to excel there.
Alternatively, PhotoZone has data on the 24mm T/S II and the 28mm IS F/2.8:
28mm IS: http://www.photozone.de/canon_eos_ff/774-canon28f28isff?start=1
And as you can see, the 28 is not too shabby. I do love it, but I just wish it had a WS gasket.
-100 to everyone who said to lock the 24-70 on 24. I know it's sharp, but it's also big and heavy.