ssh connection with public/private key pair not working on Leopard?

Solution: try passing the private key file to the ssh command using -i:

ssh -i identity_file user@server

The problem
I tried setting up a DSA public/private key pair on Leopard. but I didn't accept the default private key file name. Leopard didn't prompt me for the passphrase, and instead was prompted for the normal username/password.