Multi National Domain Address Set Issues

Multiple domains and similar content

[Whitey]

We operate multiple domains to capture local traffic in each country for around 40,000 pages each. There are some content modifications to each local site to try and provide some local athenticity in the eyes of Google and visitors.

I guess we're a much watered down and basic version of the "visit local" principle of Yahoo, again very basic version.

What are the things to look out for when putting up multi national domains.

Currently, some of the things we use/do are:
1 server [ based in US ]
interlink sites [ 1 page to 1page ]

[Whitey]

Another thought - is it necessary to do this - I mean i often see say .com site occupying No1 position in say Google local - say .ca

Is there a smarter way to appear local without managing hundered of web sites?