Trademarking doesn't give you much rights. (In fact, it usually doesn't protect the use of your trademark of others either. It's more of a "we use this name for that"-seal). However, in some cases, operating a business in the same name may. Even after the fact.
When Groupon launched in the UK, their name was squatted. The story goes that they first offered the squatter some money. The squatter, knowing Groupon was successful asked for a higher price. Groupon then incorporated in the UK, and appealed to have the domain taken over. Apparently they won. ICANN frowns upon squatters, and if you do it right, you MAY be in luck. Of course, if you're not already in business, making lots of money, you're less likely to be in luck.