If you're hangin' around the ultra forum, you're probably at least ultra-curious. While running any ultra distance is a great experience, try running at least one 100 miler in your life. Fifty k's, 50 milers, even 100k's are great experiences, but they're still races. Hundos... they're an adventure. It's impossible to extrapolate the experience of the shorter races to the hundred miler. It will change you.