In SEO terms, they are identical (unless someone searches for "com", "co" or "uk"). A UK TLD does get your site included in local results for the United Kingdom, even if your site is hosted elsewhere, so one could even argue that the .co.uk is a better extension. In terms of value if you're looking to sell the domain - the .COM is definately worth more in the vast majority of situations.
Reply I don't think its just the fact they're co.uks that get them listed in the local sites, its the content as well. I have lots of .coms with UK specific content that show up equally high in the 'search UK only' option.
In local searches, you're either in or you're not. There are other ways of being included (hosting in the UK is another), but what I'm saying is that having a UK TLD is one of the ways.
It'd be interesting to see if the opposite worked as well, taking a co.uk and filling it with content about the US and hosting it in the UK. I wonder how well that would do?
I try to buy the co.uk & the com, with the com 301'd to the uk domain. woks like a charm and always has done. Anyone who types in the com extension gets the site, and the search engines get the right geo info.
If a .com finds it harder to rank in a google.co.uk search, won't a .co.uk find it more difficult to rank in a google.com search?
No it doesn't work that way. google.com is a generic worldwide search engine, it is non geographical. Of course it is harder to rank in the .com over one of the local versions by sheer weight of numbers. The simple way to look at it is that you might be the fastest runner in your street, and the guy next to you the fastest in his. Neith you nor he can be the fastest runner in each other streets as you do not live there. BOTH of you have the opportunity to be the fastest runner in your village/block though as it is open to all the streets there.
I suppose it depaend on who your target audience is - or rather where. If your market is uk I would suggest your main promotion is with a .co.uk extension. As an earlier poster recommends I would support buying the .com as well as the .co.uk ALWAYS! If your site becomes very successful you'll wish you had done it at the time. Good luck.
And when some bugger registers the other version and sets up a site in competition to you, you will rue the day you saved a few ££'s on the domain name. If I am launching any serious site, I will make sure I have the co.uk & com versions, including the hyphenated and non hy6phenated versions.