I know it's not a great deal... but I wanted to go to LHR anyway, so I figured this would be a good "experimental trial".

The reason I couldn't book on united.com is I had credit from a previously canceled international fare.

As it turned out, calling United and telling them the routes I wanted worked out perfectly! I had a little trouble with some of the routings:

http://www.flyertalk.com/forum/milea...-question.html

but once I figured this out it was easy... the price they quoted was the price on the ITA matrix.

I'll be keeping my eyes open now for some good MRs!