[rxl]

Hey Thomas, thanks for your comments.

1) Every username system has some limitation on usernames. Look at Twitter. There are 650 million twitter users, and all of them picked usernames in the same global namespace. This demonstrates that using a global namespace is quite doable.

2) You're right, people usually have multiple Bitcoin addresses and quite a few people prefer to use different addresses for different transactions. However, the protocol is extensible and is not limited to a single address. In the future, the protocol will support a list of bitcoin addresses instead of a single address. Further, you can use a hierarchical bitcoin address and direct people to different addresses in the hierarchy. In that sense, the bitcoin address listed is just a way to identify the tree of addresses the user owns. Last, the protocol supports data to be linked to from the blockchain, so if you want, you can have a next pointer lead to an API endpoint that returns a different bitcoin address every time.

3) As far as supporting only [a-z0-9_], those are the characters that most username systems support, including twitter. Some say this is due to the fact that those are the only "word" characters. Also, using this set makes it more difficult to confuse addresses. The domain name system has similar restrictions for similar reasons. I know that international readability takes a bit of a hit, but I'm sure we'll find ways to improve the experience. We're all up for suggestions.

[konklone]

Don't underestimate how much work Twitter has to do with a global namespace. Brand protection complaints and negotiation, conflict resolution, allowing renames, allowing reuse of abandoned names...it's not trivial, and unlike the Internet (where every registrar deals with a piece the userbase), they centralize all that labor.