I use my real name on just about all of my online accounts. I sometimes wish I hadn't, but that ship has sailed. I keep most of my social media accounts as locked down as possible, and I've deleted a lot of them.
Github is interesting because, in the case of really popular projects (which I don't have, so this doesn't apply to me,) you probably want the project name to be the namespace, rather than the developer name. I personally find it a bit annoying that this isn't more common, but I understand why. Who wants to manage a separate account for each respository?
>do you think it is unprofessional to use anything other than your name?
If you intend for people to pay you, it's professional to use your real name, and not present yourself as a persona. Otherwise, I don't think it matters, but you shouldn't expect people to take you too seriously if you publish code under an immature or ridiculous pseudonym.
> do you have any thoughts or opinions on the "branding" (I hate that term, ftr) of developers and our community as a whole
We need to be better at selling ourselves, rather than letting ourselves be sold. Much of the modern branding behind dev culture was created by marketers as a way of exploiting naive, young talent, in a similar way that the "American Dream" was created to exploit immigrant and lower-middle class labor.