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1. Continental Airlines and United Airlines are owned by the same company and are in process of merging. Continental will leave Membership Rewards in October 2011, and cease to exist sometime in 2012. Today you can transfer Membership Rewards points to CO, and immediately transfer from CO to UA if that is your preference.

2. However, it is not necessary to redeem miles through the airline on which you wish to travel. Most airlines belong to one of three international alliances. You can redeem through one program for travel on any airline in the same alliance. For example, you could transfer from Membership Rewards to British Airways and redeem for travel on any OneWorld member, including American Airlines. Both AA and BA offer one-way awards which makes it straightforward to construct a trip using AA miles for some flights and BA miles on other flights.

3. In addition to miles you need to think about other costs. Award tickets are not "free" flights. You will pay taxes, and some programs (including British Airways) apply fuel surcharges on award travel. In particular, departures from UK airports are subject to Air Passenger Duty which all airlines pass through to passengers. The combination of taxes and fees can total several hundred dollars per person.