As a guess, I think the domain name would probably be more important than the location of the IP address. As pricing and services for foriegn hosting companies becomes more competitive, businesses are starting to host with servers that are not in their own country, making the host IP address location meaningless (after all, how many small businesses host their own web servers in their home towns?). I would be very suprised if Google considered the physical location of the server. I would not be suprised at all if they did take into account the top-level domain, and possibly even the language of the linking page.

I just had a terrifying thought though... I keep getting ads from SEO companies promising top ten ranking in Google for the keywords of my choice... I notice they don't specify Google.com...