Well I just tried it from home and it barfed on my UA record locator (which is all I have), but it at least got that far. It then asked me for my name and destination and found my itin and let me check-in.

And god bless the Star Alliance - my Exit Row seat was safe! And I have an empty middle next to me! On a flight that's pretty close to packed! Not sure if that middle will stay blocked, but I am happy I can watch movies on my MacBook and not be crammed into a 31" pitch row. ^