Been once. Love Edinburgh. It's awesome in the fall, awesome in summer, but the one time I went in August, the Festival, the Fringe, the Tattoo. It's like carnival, but colder. Love the city, the people, the beer, the American food at the International food festival at three sisters. Colgate. Much fun. The Tattoo is shockingly cool. Papers, drums, and a smattering of performers from the Commonwealth. Steel drums from T&T, zulu dancers, Maori from NZ (love Kiwis). One Service is honored each year and the show is always cool. Saw Royal Marine Commandos put on an impressive display. Show started out a bit hokey with a living museum type display, then blacked out as they staged a mock assault under green lights with sniper teams on the stair two seats from me, rubber boat insertion, took out sentries, and “blew the enemy camp” with a firework. It's cools. Ends with a one two punch of the massed pipes and drums, and the lone piper in the castle walls lit by torches.
Also been to Edinburgh on a Tuesday in October (or some random time) and met great folks. Also, London, Cardiff, Swansea...some towns in Devon. UK has amazing people. If you can go, you should, and meet locals, and do local things.
I'd love to see the US, UK, Australia and Canada form the largest, most prosperous and greatest alliance the world have ever seen...again. In UK, Americans can really feel at home.