There is an excellent guest article at Search Engine Land named The Curious Case Of Google's Bizarre UK Search Results. In this write up, Bas van den Beld explains some of the recent history with what is going on in the Google UK results and shows specific examples of why he is upset with the results.
Let me catch you up, because it actually goes a bit further back than what Bas explained. In April of this year, folks at WebmasterWorld noticed that the Google UK geo targeting algorithm might be a bit off. Maybe this was an early sign or test from Google, because those signals went quiet until June, when the Twitterverse went nuts about the UK Google search results. In fact, in July, Google tested removing the pages from UK radio button, which upset a lot of people.
This was such a big deal that Matt Cutts created a video about it:
In short, Matt explains that Google UK is now showing a lot more US sites (i.e. dot COMs) in the UK results. In the past, Google typically showed more .co.uk results, but now Google is "getting better" at showing relevant .com results He added that this change, Google will "likely not revert," so we might be stuck with it.
In any event, many UK SEOs are not happy about this and they have expressed this on Matt's video, via Twitter, forums and in blog posts.
Forum discussion at Sphinn.