Does the fact that he is publicized really make a dent on participation? I would say no.
participation is minimal at events (50+) unless it is a big one like western states or another prestigious or historic race and guys that are 40+ are still on the top of the ultra scene here in the US. what does that tell us? the sport is not growing.
I think most people wont take it serious because guys like Scott are few. (guys that are actually impressive with pace over these distances). the others are just getting out there and doing what others just dont want to do. not to mention the fact that the runners involved with ultra are seen by most other runners as being really bizarre. social ackward, etc. Most runners (5k-marathon) would probably not consider what most of these people are doing as running.. In my opinion, if you can take a nap during a race, it ceases to be a run at that point.
Karnezes is a shameless self promoting media hog and is not an impressive runner by any stretch in my opinion. i do commend him on being able to get the attention he has for doing nothing.. :)
my .02