This is a bit of an old question from and old timer but I'm wondering if anything has changed...
I used to run different versions of my site, keeping .co.uk and .com separate. I don't remember why but some time ago I merged the two together into .com and show different things to visitors depending on their I.P.
As I understand it, Google will mostly (only?) look to see what's on the U.S. I.P. version.
For the most part that's not a big deal but there are advantages to my getting them spidered individually again such as showing the best selling products by country. Also, there are some language issues. We've recently launched a gift voucher but that's gift 'certificate' in the U.S. As it stands I can't optimise for both so I'm limited to one (the U.S.).
If I do split the sites, how different do they need to be for Google not to mark them down as duplicates and bar one of them?
Any thoughts appreciated.