buckworks - 12:52 am on Aug 27, 2011 (gmt 0)
Definitely, get professional advice about trademark registration for every country where you think you might eventually do business.
later in a month , someone from other place , say Canada register "mysite.net"
If that happens, you have been negligent.
Take the commonsense precaution of registering the most obvious domain variations for yourself, right from the beginning. Don't leave an important one like "mysite.net" open for some outsider to register!
Try to register Example.com, Example.net, Example.org, and Example.tld for your own country. Also, for the .tld which will you will use for your main site, register predictable spelling errors, and the hyphenated version if your domain name contains more than one word.
Try also to register Example.tld for countries which use your language, or where you might think of doing business later. If need be, get local legal help for countries which restrict ownership of domains by foreigners.
Cover the basics but don't become obsessed about registering every possible variation. There comes a point where you could spend more on defensive domain registrations than it would cost to sue the occasional squatter who registers one that you missed.