On regular Unix systems, you’d do
export PATH=$(PATH):/usr/local/mysql/bin
when adding the mysql programs to your path (exporting the environment variable PATH).
On Mac OS X (Leopard), you have to add /usr/local/mysql/bin to the file /etc/paths (edit it as root). Restarting Terminal is enough, no reboot needed.
boskabout 
You can just add it to your .bash_profile too of course, no super user necessary