Well, having made the same change, from XSi to 7D, I can tell you that the learning curve was steep. Learning the AF system and what to use when, as well as the sensor points, was a bit of a climb. I'm not shooting much right now, so I'm a bit out of practice, but certainly a lot better than when I first started with it. I've got to get rid of my cheaper glass, and hoping to get the 24-105 to go with my 100-400. I'm not sure my 100-400 is calibrated quite right, but I am also not very stable when I hand hold or pan, so could be me. Even the tripod stuff isn't as sharp as I think it should be. I should just give in and send it in while I still have the XSi.