My overall point is the same: I haven't experienced any anti-American sentiment personally, but there is at least some current of anti-American feeling in the UK.
I think you are right, and there are two factors in the rise in anti-US sentiment in the UK:
Firstly, we Brits have also been increasingly targeted with anti-Brit sentiment from other nations over the war in Iraq, and we've noticed it. A clear majority of Brits are against the Iraq war for a number of reasons. However, rather than accepting our country's own responsibility and taking our anger out on Tony Blair & co (where it belongs), we join in with the yank bashing, pretend it was all your idea and that our planes and troops ended up bombing the sh*t out of Iraq through no fault of our own. This 'blame shifting' is not an attractive trait.
This is compounded by...
The BBC (and other media elements, but especially the BBC). The current affairs and documentary programming areas often seem to be gripped by anti-US and anti-Israel sentiment that leads to inherent bias in the way these countries are portrayed. Just watch BBC current affairs (and documentary programmes with any kind of political overtone), and just count how often you see an Israeli or an American who is left wing, moderate, secular, and tolerant. It's pretty rare. This portrayal of the US as a country full of foaming at the mouth uber-patriot warmongers creates a negative sense of 'us and them'.
Just my theory... criticsm / thoughts welcome!
Whilst our group was walking through the streets a small group of 20-something males across the street just shouted "English, pah" and spat on the floor.
I don't think there's much love for us in parts of the old Yugoslavia for not stopping the genocide soon enough,
On the contrary, I'd be willing to bet money that they were Bosnian Serbs, who (as do many Serbs in Serbia and Kosovo), resent NATO, (particularly the UK and USA who did most of the actual bombing) for our role in Kosovo.
I don't think the Kosovan conflict was all we think it to be. The simple fact is, before the conflict, Kosovo was a province of Serbia and had many Serbs living there, and now, it isn't, and there are none. Kosovo is virtually pure Albanian. Now that, to me, sounds like ethnic cleansing, but isn't that what THEY were accused of? Whilst I am certainly not defending Serbs, I feel all is not as at seems there at all.