Indeed! Consistency of my brand is incredibly important. Ideally the end goal is to be able to simply list icons (fb, twitter, instagram, pinterest, tumblr, wanelo, etc) and have it understood that my business name is consistent in all of these places without having to provide full links - although I do provide full links on some materials, depending on my demographic ;)
This also applies to your logos and avatars across multiple sites online - Be recognized!
This not only creates a pattern of recognition, but also helps establish you as a business that has been (or has the appearance of being) around for a while, where you were able to snatch these usernames early on.
I would at least recommend scooping up your name on the larger sites, even if you arent using it yet, so that you dont lose the opportunity to do so in the future.