I did Couch to 5k at the end of last summer and had to repeat the first five weeks. After that it got much, much easier, but yeah, if you're not accustomed to running at all (even if you're fit, which I was), it can be a challenge. It's the first time since high school that I've been able to get into running without doing something to my knees or ankles. Yesterday I ran 7 miles. And liked it. I hated running until very recently. I'm still super slow, and probably always will be, but it makes me feel really, really good.
I'm planning on doing the Salt Lake City one in June. It will be my first race!