SQL Server login character length

Run sp_server_info procedure to find the limitation of the server with other information.

e.g. EXEC sp_server_info

Ref:
http://awesomesql.wordpress.com/2009/08/21/maximum-length-of-loginuser-name-and-password-in-sql-server-2005/
http://msdn.microsoft.com/en-us/library/ms176094.aspx
http://social.msdn.microsoft.com/Forums/en-US/sqldocumentation/thread/7b28762b-5e7e-40c7-b765-3eb6c2681ba5

Other limitations:
http://weblogs.sqlteam.com/mladenp/archive/2007/07/24/60267.aspx