A thread at IHelpYou Forums named Server Location resides in the Google Forum, but in reality, it applies to all major search engines. The question the member asks is, would it improve rankings in Google.com if he moved his server from the UK to the US?
He explains that he is "currently at No.4 on Google. I am behind two very large directories and about.com." In Google.co.uk he is second, ahead of two of the directories outranking him on Google.com. He continues to explain that he uses a .com tld. So he asks, "Would it be a good idea to move the site to a US hosting company, would that help me get nearer No 1 for my KW on Google.com or would moving hosts hurt my position in the short/long term?"
Very good question. And very good advice in the thread. Moderator Quadrille explains; "I think changing horses would probably be just about the last thing on your mind, unless you are looking very specifically at a US audience, and the UK audience is of little value to your site."
Many of us don't think about our audience and who we are trying to reach. If you have a site targeting the UK based audience then ranking well in a UK flavored search engine will rock. But if not, and if you want to rank well in a US based engine, then by switching to a US server farm, it can't hurt your US rankings (well maybe it can, depending on other variables). It can only slightly hurt your UK rankings but potentially improve your US rankings.