I'm always delighted to find a match from the British Isles, so thank you for testing.
The known ancestors of people whose kits I manage are all from the British Isles from two to four generations ago, so UK/Irish matches are very useful for us.
Although I'm in Canada, I'm really in the same boat as Cockneyrebel - grandparents all born in England and emigrated without extended family -- so I'm not really looking for relations in the US (or Canada).
But with a surname as common as the one I had discovered my great-grandfather was born with, I had hoped that a match in the US would solve two birds with one stone -- I would confirm that my gr-grfather really was the son of his registered father, through a match with that surname, and at the same time, some lucky people in the US would finally know where their male-line immigrant ancestor came from, because I do know about my gr-grfather's ancestors in Cornwall back to the 1700s generally.
Since his father was connected with mining in Cornwall, and mining-related emigration to the US from Cornwall was common, I felt sure I would find a match among the many hundred people in the project for his very common surname. Nope. Not a sausage. Not a remote match. I was almost as disappointed for the people his DNA could have helped as I was for me!
But the very close match I did find gave me yet another surname for my gr-grfather (or his gr-grfather, or whoever), and confirmed for the match in the US that her father (who knew his grandfather had emigrated from the same part of Cornwall circa 1850 in connection with mining) was legitimate despite the family rumours, and despite the lack of an actual surname match.

The fact that people in the US, in particular, are unaware of their Old World ancestry doesn't matter when it comes to DNA matching -- that is exactlly what they are trying to find out. The matches, if there are any, will be made (e.g. at FTDNA) regardless of surname or family history knowledge. And then the people who match get to figure out where their trees converge. Whether that is helpful to the tester in the UK depends on what they are wanting to learn.
So I absolutely encourage it too!