Yikes, I just read Autodesk's "terms of service" agreement.
Anything you create with 123d, and post on an Autodesk website (and perhaps anywhere online,) is theirs, with which they can do whatever they want. That's a bit more intrusive than SketchUp/Trimble's terms-of-service, which provides that your intellectual property remains yours.
It also appears that using 123d automatically transmits launch, close and command-use data, so, internet-connectivity may be required. Matt, have you found this to be true? (Maybe, this is only during beta?)
I am, at least, interested in trying it, but some of Autodesk's conditions seem rather intrusive.
-Taff