One of the best ways to avoid typing your passphrase (if you have indeed protected your private key with a password!) is to use SSH Keychain. This handy utility allows you to:
store your passphrase in your Apple Keychain
set session environment variables (e.g. setting HISTFILESIZE allows you to increase the amount of command line history bash keeps around)
set up tunnels
After you download it:
Copy it to Applications/Utilities
Open System Preferences
Select Accounts
Select your account
Select Login Items
Add SSHKeychain to it by selecting the + (plus) button
Check the Hide box if you don't want it to show up in the Dock
From SSH Keychain preferences, you can configure things like were icons appear, how to handle security, etc.
-- DarrellSchiebel - 27 Nov 2006