It is always good to have your brand name (letter-for-letter, if possible) on all of the social sites out there. This way nobody will be interfering with your ability to get your word out there without any confusion.
Even if you don’t plan to use any of those sites, you’ll want to “lock-up” you keywords. Each place where another person has your exact keyword it takes away from you standing-out as much. So if you can create a brand name that nobody has or thought of – you’d be in much better shape.
I was very fortunate with “buyadpacks” because nobody was using it.. in ANY of the social networks or blogs, etc. I got lucky.