For reference, RFC 2812 (the update to RFC 1459) says:

Quote:

1.2.1 Users

Each user is distinguished from other users by a unique nickname having a maximum length of nine (9) characters. See the protocol grammar rules (section 2.3.1) for what may and may not be used in a nickname.

While the maximum length is limited to nine characters, clients SHOULD accept longer strings as they may become used in future evolutions of the protocol.