I'm new to canon and along with my new 5Dmk3 I am also breaking in some awesome new L glass. I will agree that I was a bit disappointed with what seemed to be soft images at first, but I quickly realized that the focus was a bit off on both lenses. I just did a little micro adjust and it made a HUGE difference. I bought the SpyderLensCal a while back and I know that it is way overpriced and I could easly build one for next to nothing, but the convenience of it almost mitigates the annoyance of micro adjusting. Just shoot, review, adjust and bang your done. I think this may be the cause of the discrepancy of so many different people either saying they are getting sharp images or not and then attributing it to the camera body, DPP or JPEG engine and saying maybe I just got a bad unit. If the camera was back focusing by just a little it would be really hard to tell it was not just a soft image because you wouldn't see the sharp in focus region. Anyway, try checking for focus adjustments I've noticed a lot of the people getting good results on other forums are noticing this as well. Nice thing is you can also enter in the serial number after you adjust a lens and it can store up to 40 individual lenses, so hopefully once you get one dialed it will be go for a long time.
if your curious about the lens cal thingamajig here is a link to a vid of how easy it is to use, or it will give you a good idea of how to make one yourself.http://spyder.datacolor.com/learn_videos_spyderlenscal1.php