My domestic travels will be unaffected by the war, and I'm 99% sure I will still do the 15 April trip to LHR - even if we are at war. I'd avoid the Middle East and many Third World countries if I had plans to visit them in the next month or two.

I feel comfortable in London (I'm there 4-5 times per year), keep a low profile, and avoid standing out as an American (use hotels and restaurants frequented by locals, wear shoes and some clothing purchased in the UK, etc.).

However, terrorism aimed at the airline industry would be an entirely different matter.