Aside from the lack of scrolling (wow, that's irritating), my biggest problem is that it's in Silverlight, rather than the rather more universal Javascript. It means on most computers, I'd need to download something before I can use it, which kinda diminishes the value of having it online. Plus, Gmail is so much more responsive than the CB, it isn't funny.
Second big problem: I imported my level 19 shaman from my Dark Sun game... and I can't give him his Elemental Priest theme. Or sort him out as a Dark Sun character. So that's irritating. Then, when I go to build him as a new character (which takes quite a long time), I can't take his Invoker MC feat. (Yes, I know, but even the DS book mentions corner cases it can be allowed.) Like, it doesn't list it as homebrew or anything, the option's just not there. That's not really cool!
I'm not going to say this will drive me to another game system or anything... but I'm definitely keeping the old CB installed. I'm sure this will get better in time--one month from now, I expect it to be quite nice.