One of the questions that I'm often asked is 'should I use Google.co.uk or Google.com?' It's an interesting question, without an obvious answer. If you search the local version of Google the idea is that you'll get local results, so a search for 'football' will give you soccer results, not American football information. However, Google is intelligent enough to know what the computer IP address is, and will give you local content anyway - it doesn't matter if I'm logged into my Google account, or I am logged out, I'll still get English football related content. If I do anything that Google considers to be a local search, such as 'library' I'm going to get links to local libraries and a handy little map to go along with it. (Though to be fair, if I'm not logged into my account, this option isn't available.)
However, if I'm using the .co.uk version of the search engine, I'll come under the 'right to be forgotten' ruling, which means that some content may have been removed (if you're not familiar with this, I wrote a blog post on it some time ago) which doesn't really cause me an issue, but it's a vague irritant - it may not bother you of course.
Google however, thinks it's a big deal, and they're starting to make it harder to get to the .com version. If you're using the .co.uk (or any other local version) you always used to get a link at the bottom right of the screen offering you the opportunity to go to .com, but this now only appears the first time that you go to the site - after that, the link disappears. You have to type in the .com address into the browser address bar to get there. Now, you may feel that this isn't a big deal, but given the way that Google is trying to push its users down particular paths (we're seeing it all of the time with search for example), it's a interesting albeit somewhat worrying look into a potential future in which we are automatically piped to one version or the other. You can get around this however - either with the simple expedient of remembering to go to .com or by adding http://www.google.com/ncr into the address bar. This stands for 'no country redirection' and should mean that it's not necessary to keep having to find .com in the future.
In summary, it's not a major issue, but if you are working with people who are searching using Google, it's worth mentioning the different country versions, and if they particularly prefer to use the .com version and can't seem to find it, now you know!