One word of advice- AVOID LHR!

I used to be based in LHR and I remember seeing 300+ nonrevs stranded for weeks on end. I remember once in the summer of 2002 I left LHR going to LAX. It was a 3 day trip. When I returned from the 3 day trip I had 2 days off followed by a ORD trip. When I was walking to the gate for my ORD departure, I saw atleast 30 of the people that had tried to get on my LAX flight 5 days earlier! They had been bumped and rolled for 5 days! When I would come back to the USA from LHR in the summer I would almost always end up on the jumpseat as every seat would be occupied.

As others have mentioned, buddy passes are waaaaay down the pecking order so when the flights get full and nonrevs start stacking up it can get nasty. UA did have an embargo on most European travel for buddy passes last year. I have yet to hear or see anything to indicate they are planning the same for this year.

Best of luck-

-IFLYUA