I've been meaning to write about something like this but Jason absolutely nailed it.
I've been running for fun for a while.
If I don't feel like it, I don't go. If I feel good, I just keep on running Forrest Gump Style.
If running is painful, that's OK as long as you are having fun with it and you aren't injured.
For those of you just starting out with C25K or similar plans, use them if it works. My advice is to just go out have fun and run when your body tells you that you can. You will be up to 5K in no time at all. Hell enter a race anyway and walk if you need to but run it with a good friend to share the experience.
Barefoot Running University » Run for Fun: A Running Plan for the Rest of Us