I imagine that most people will be searching for a local / national site rather than an overseas one and think that .com will give US based results. Actually Google and Bing both redirect to their .uk sites from within the UK.
It is that they prefer a .co.uk result to a .com result in the SERPs when presented with a choice.
Apparently EURID have been doing some similar research and their results are that the local cctld is always preferred to .com with .eu lagging behind. (I haven't had any corroboration of this research though)
I also know that Nominet have a vested interest - but would tend to believe them, they just wouldn't have made capital out of the results if they hadn't been in their favour.
Eurid's research is Mickey Mouse stuff that's only designed to make .eu look good. They used what's known in the Search business as the Infinite Monkeys approach. They got a pile of students to evaluate a small sample of websites and slathered a bunch of statistical methodology on top. I run a websurvey of the Irish webspace (approx 250K websites) every few months (not sure if I can post the results URL) and .eu usage is much lower than ccTLD or .com in Ireland. The last time I did a survey of .co.uk websites, the percentage of active .co.uk websites was much higher than that of .eu ccTLD. (Both these surveys had samples of 1.5 Million plus websites in each ccTLD from what I remember.)
These are the stats of Irish hosted .eu domains/websites for May 2010. The Percentage is given for websites in the survey and for the sites represented as the number of domains.