I have hit a wall in my running. For the last couple of years, I've been able to run a half marathon at about a 8:00 pace, and a full at about a 9:00, but I can't get below that. I've heard that interval training is the way to do that, and remembered a thread from a few months ago by Archaea:
http://cougarguard.com/forum/showthread.php?t=19709
I was just going to steal his workout unless someone can give me better advice.