"Client does not support authentication protocol requested by server; consider upgrading MySQL client"

Did you just upgrade MySQL and got the error message:

Client does not support authentication protocol requested by server; consider upgrading MySQL client.

MySQL 5.1+ uses an authentication protocol that is incompatible with older clients. The best solution is probably to upgrade your mysql client, but there is a quick an dirty fix if want to continue using your old client: You can reset the password to the pre-4.1 format for each user that needs to use an old client program:

mysql> SET PASSWORD FOR 'username'@'localhost' = OLD_PASSWORD('thepassword');

More information available here:
http://dev.mysql.com/doc/refman/5.1/en/old-client.html