I've booked over a half million miles of awards on LH, SQ, and recently with NZ, booked using UA MP miles.

They only have limited inventory with their partner's seats, yet still was able to accomodate requests for 3 passengers together, for instance.

Regarding USA domestic: During fall '05 I unfortunately had to spend 40K for 2-3 awards on UA versus the typical 25K...that was the only period of time I had this unfortunate circumstance. But remember UA was basically "alone" for domestic travel west of the Mississippi River. In the past you had the option to use UA miles for Delta (more options to route a trip). Soon they will get US/HP to help out immensely.

For those just starting out I'd also say the AS program is okay as you have the chance to find seats on AS, AA, NW, maybe CO and DL as well?

Edited to add: UA does not charge "expedite" fees for cashing in an award very close to travel. I've ticketed awards 3 hours before departure - no expedite fee. AA and AS both have this fee (I believe $60/ticket). UA does not charge this to anyone, even a zero-status member.