More Important facts about awards

Award travel must be on a United or partner flight routing exclusively between valid cities or continents described in the United and partner awards charts, with no connections or stopovers on additional continents (or cities, where appropriate).
Travel on code share flights operated by other airlines is excluded.
All flight awards are valid for roundtrip travel. If you choose to use an award for one-way travel, no residual credit will be issued for unused segments.
One stopover en route to your final destination or one open jaw is permitted for a flight award on United between the continental U.S. and Hawaii or between the U.S. and the Caribbean, Asia, Australia, New Zealand, Central and South America or Europe.
When traveling on an upgrade award, a maximum of one stopover en route to your destination is permitted.
When United award travel originates in Asia, Australia, New Zealand, Europe or Latin America and entails routing via the U.S., two awards are required: one to/from the U.S., and another between the U.S. and your final destination.

http://www.united.com/page/article/0,6722,1140,00.html