Is this a Nikon 12-24 ? Cool. For 1.5x sensor, this gives really wide angle perspective ? Only downside is that it might now work with a Full frame sensor down the road (but propably not a big deal as for it to come down to an affordable price will take quite some time).
I also saw some great reviews on Tokina's similar offering. Very tempting. 17-40L is good but on 10D it's only about 28mm, not wide enough. And honestly, most of the time we use this lens for landscape almost exclusively so a wide coeverage is very handy.