There's a lot of information on the intertoobs about getting ssh-agent "working" in OS X and even more articles about when and how the stock behavior of ssh-agent changed (mostly with respect to how ssh-agent interacted with the Keychain).

This article doesn't cover or care about any of that.

This article is concerned with:

• Enabling ssh-agent in such a way that I can "ssh-add" in one terminal window and that same agent (and the loaded keys) is available in all of my other terminal windows.
• Enabling use of ssh-agent from MacPorts and/or Homebrew and not the older ssh-agent that OS X ships with in /usr/bin.
• To avoid having to put my keys in the Keychain (just a matter of preference).

The worst feeling for a geek:

This has happened to me twice now: upgrading Mac OS X from one release to another and after the dust settles, the search function in Outlook 2011 totally breaks and always returns "no results". As we all know, email sucks and being able to deftly search through that mound of crap in your mail client is the only thing that makes it somewhat bearable.