I tried two copies of this lens on a 20D, then returned both of them. For $1100, I expect to be wowed. The lens wasn't sharp enough, the colors didn't stand out, and it didn't auto-focus very reliably at all. About the only good reason I can think of for getting this lens is for low-light usage, and that's not enough for me to spend $1100.

I played with a couple copies of the 16-35mm f/2.8L, then ended up getting a 5D and the excellent 35mm f/1.4L (35mm is like 22mm on a 20D).

In all fairness, I didn't try the 24L for any landscape work - I've read that it focuses better for far subjects. I also never tried it on a 5D. This lens doesn't get nearly as much good press as the 35L and I think there's a good reason for that. Still, I'd like to rent it for my 5D before forming a final opinion.

Finally, the new 16-35 f/2.8L II clearly beats the 24L in sharpness, so there's even less reason now to own the 24L - basically for those who want to use it at f/1.4.

I recommend the The-Digital-Picture.com for comprehensive reviews.