Use domain name extentions to emphasise geographical relevance for SEO...

Having a relevant domain name extention is quite advantageous for SEO. For example, if I have a .UK domain instead of a .COM domain, then I'll stand a much better chance of ranking well in the Google UK search engine.

The benefit of such an increase in relevance to Google UK is mitigated by a corresponding decrease in relevance to Google.com (which is most relevant to USA). But if you're overwhelmingly targeting the UK then it's worth it.

But if you can't switch to a UK domain name, used a UK-based web server which is almost as good a signal to the search engines that your site is relevant to the UK.

Example 1: SEO

I just went to Google (on 3rd October 2009). Google automatically detected that I'm in the UK and sent me to Google UK. Then I searched for SEO. Notice how 3 of the top 5 results had UK domain name extentions.

This is because Google assumes that UK sites will generally be more relevant to me than non-UK sites, because I'm using the Google UK search engine.

Screenshot of Google UK, search for SEO, and find .UK