Attempting to login with a ridiculously long name will, at least on mac OS, trigger a System.IO.PathTooLongException: http://pastebin.com/FjAMvw7g

However even using an unreasonably long name is currently possible:

• http://i.imgur.com/lga07j9.png
• http://i.imgur.com/GodUq1R.png

I think it would be more reasonable if you capped the length of the player's name to something like 16 or 20 characters, and hardcoded the server browser Player Name field to only hold that many characters (so even pasting in a long name should just be cut off).