Attached to my 350D and always stays there.
Have to be picky when buying this one. The first one I tried out (code UW) was soft even at center (F/4) and has high CA on extreme edges.
I'm not sure about fullframe, but this lens gives decent range, which is more preferable over speed to me. Shoot some sports and portrait. It works really great outdoor, but not so good in low light.
Right now I don't need 70-200 F/4 IS I planned to get any more.