Don't be surprised if you get put on the limited-view list (no offense, but I'd like to keep some parts of my life between myself and those who experience it firsthand with me), but feel free to check out facebook.com/nicktabick.
I'll give Facebook a day or two to calm down and I'll try it again. I have no clue if it will stay like this or what. I wish it would because like you, I didn't seem the option to create a custom name. Obviously it was there because I'm seeing custom names popping up all over.
I assume they take a similar idea to considering the period as most major e-mail providers, hence why the period is cosmetic-only. (Once you get to your profile, the links will all point to your username as you specified it, though.)
And, for the record, there was a custom name option tucked away under a 'More...' link.