Not to rain on anyones hard work but one needs to compare ones own photo's of a genre with the same taken with top end Nikon & Canon models and generally you will find that the fast moving (especially head on) shots taken with Pentax lack the sharpness & "bite" so to speak.
Yes you can pre-focus on a spot etc etc but I'm talking about focusing speed when things sometimes happen out of the blue e.g. a buck suddenly springing out of the bush at full flight with a lion chasing it
This happened with my son borrowing a friends D90 and every shot was in pin sharp focus - to be quite honest I wish a Pentax had such a good af.
Trust me I'm a die hard Pentax user but having used the "autofocus" on the D90, D300s & 7D it's a no brainer which system is leagues ahead.
If I was planning on using a dslr to earn money from sport photo's it definitely would be a Canon or Nikon
Some downhill mtb images
Downhill Mountain Bike Images - Photography & Digital Camera Forums