I don't think it's meant to be super competitive - everyone gets the same medal. I've heard of others who have walked the entire 5K. The other thing to keep in mind is that you can walk the course any time during the day if you don't care about the medal.
However, I've also heard that they only give out medals to those who complete the 5K within a set time - some have said 45 minutes, others have said an hour, yet others have said different times. I'm shooting for coming in under 45 minutes. I don't know if I'll make it, but I'm going to try.
The
DCL website has very little info on the 5K, so I don't have many answers. Search the boards for info. With runDisney taking over the CC5K, I really don't know what to expect. I've got a bunch of questions for Guest Services when I register, hopefully they'll have some answers! Otherwise, I'll find out the morning of the run.