Just back from 4 nights in London. It was my 5th visit since 2003, but this time the dollar's weakness was palpable. Small example - yesterday at Paddington, waiting on the Heathrow Express, $8.86 for a double cheesburger and a water at BK. Oooff!
It's still manageable if you really want to go. Just be ready to watch your money evaporate faster than you thought possible.