I bought this lens to complement my 5D (full frame body). It works fine, but it has VERY noticeable barrel distortion at the 20mm end, where I would be using it most. It IS a wide angle zoom, after all.
If you are shooting buildings and/or interiors like I do, don't bother considering this lens.
I had a Sigma 12-24 (full frame) from my 10D/20D bodies (1.6X) and that lens gives me much better results at 20mm. Being able to put a polarizer on the front is nice, but not at the expense of barrel distortion.
For landscapes without buildings or other man-made objects, it might be just fine, but not for buildings.