Good question. I am toying with the idea of transfering a couple hundred thousand miles into Continental. My thought is that those miles will subsequently merge into my United Mileage Plus account. Currently DL/SkyTeam is my carrier of choice, but everytime my employer forces me to use United, I have had good luck using miles to upgrade on international routes. Currently when I fly UA, I'm still subsisting off the last few hundred thousand miles remaining from a Diners Club transfer when they severed their relationship with UA. Adding to my UA account with an AX MR transfer via Continental could give me a useful injection of new miles to use for UA upgrades.

I would clean out my MR account in a heartbeat and transfer them to UA if that would help me obtain Million Miler with UA--I think you may be asking this question looking for those types of deals. Alas, I don't think there's any backdoor way as there may have been with TWA merging into American because my understanding is that AA is the only carrier that considers total credited miles on the account toward lifetime status. The other carriers including United only look at elite qualifying miles.

For a Star Alliance award ticket, I know you can transfer miles into any Star Alliance partner to redeem and some have better redemption levels than UA. However, to upgrade on UA, you need UA miles. Thus, with no status currently on UA, it has proven extremely valuable for me to find roundabout ways through Diners Club and now possibly via Continental where I could move miles into the UA program. Every flight I have taken over the last five years on UA has been a Y ticket. For full fares, United is extremely generous, asking only 5,000 miles one way domestically and 10,000 miles one way to Europe to upgrade from economy to the next class of service. So far, I have been lucky enough to obtain a mileage upgrade for every UA flight segment I have attempted. Just not sure whether the CO merger will make that more difficult on the international side.