I have a busy site and we want to host it in multiple locations for SEO reasons. We noticed that even though we rank great in Europe our US content doesn't rank well in the US. This could well be due to the fact the domain is hosted in Europe.
Here are the options I can think of:
1) Serve US content on a US server. Serve rest of the world content on our EU server. Downside: no physical access to US server. Keeping a copy of the US content on the EU server would be buggy. The DB is 50GB
2) 301 US users to US.Mydomain.com and mirror all the content there. However we would be showing Google 2 different URLs with the same content depending on where Google made the crawl from. How should Google treat it in SERPS? Would they be smart enough to index US.Mydomain.com on Google.com and www.Mydomain.com on other Googles like Google.co.uk?
3) Keep all the content on Mydomain.com and serve the US content from US servers. Would Google even notice? After all that is the whole point.