First, I agree that having the "check all" button checked by default (but the items are then not checked) is confusing. Non-standard behavior is probably not a good thing. Better to leave it unchecked by default unless you intend to include everything by default.
I tested zippiness by just selecting everything. The invert checkbox wasn't obvious, either. I'd like to suggest moving it below the folder and renaming it "include subfolders", a la Windows. Same function but again emulating what others have done.
Is there a reason why there is a "Continue" button and a "Get XML" button, in separate places? It seems more logical to me that at that point, Get XML is the next step at that point. (I hit continue by accident and didn't notice the Get XML! button. Because people don't read instructions.)
The Wizard was very zippy at generating the XML button.
This feature is going to be very cool. I love the idea of cloning the best stuff out of a good Conversation. Will the Wizard in the future include e-mail or the newsgroup?