There's a whole lot of name calling on here and not enough organized debate.
For those of us who majored in something other than exercise phys, what the heck is type IIx?
Are we talking about some fast twitch fibers being fueled by glycogen and being more and explosive vs. fast twitch muscles that are fueled by oxygen and have more endurance (but not as much as slow twitch)? I read something like this in Better Training for DIstance Runners.
I also think it's very individual whether or not distance running hurts your speed. I sure don't think it's hurt mine but I do know some guys that just cannot bust a quarter like they could in high school. I doubt Pter Snell's sprinting ability was hindered by his 150 miles/week. I do think my jumping ability has suffered over the years (I'm still just 23 by the way).
Either way I think 2-3 miles here and there is not a bad idea for sprinters just so they can get through a longer sprint workout without coughing up a lung.
How you run your miles and what you do to maintain your speed in conjunction with your basework matters a lot too.