I was checking the system logs on my iMac (something I do every once in a while to make sure nothing’s amiss) and noticed a lot of lines such as this:
10/13/11 3:46:14.887 PM com.apple.launchd: (com.apple.Kerberos.kdc) Throttling respawn: Will start in 10 seconds
(I broke this up to make WordPress happy; in reality the above is a single line in the log file).
launchd was trying to run a Kerberos (i.e. authentication) related process, and repeatedly failing. I am pretty sure that this started happening after upgrading to Lion.
Anyway, there is a quick fix, thanks to this post by Craig Newell in the Apple support forums. From the Terminal, issue the following command:
(you then have to enter your password). This fixed things for me. See the aforelinked post for a brief explanation.