I would expect Google to have tied that phrase up in so many legal loopholes that the moment you tried to use the domain they would drown you in paperwork. http://en.wikipedia.org/wiki/DoubleClick
You're kidding, right? If you set up a business and call yourself "double click" you run a really high risk of being associated with the Google ad system and leveraging it's reputation. I don't care if your domain is doublecli.ck, double.click or double.click.com, unless you are selling tractors or cup cakes you're in a world of trouble.
Yeah thats right if he/she tries to establish same biz. I don't know what's OP's intention, but I replied on the basis that 'double' is just a generic keyword. But definitely 'double click' as a keyword could be problematic.