If you cannot login any longer from your Mac user's shell account to a remote server with ssh, and ssh -vvv loginname@server is hanging at the following line...
debug3: Trying to reverse map address 192.168.73.23.
..then look cd into /tmp/.KerberosLogin-xxx-yyyyy, where xxx is your Unix user ID (typically 501 for the first user created on the machine), and yyyy is a random number. Once there, remove the file named KLLCCache.lock. Try again, and bingo. Hurray!
Mac OS X Hints
http://hints.macworld.com/article.php?story=2006020803085942