For anyone interested I thought i would follow up on this and let people know my experience with this catch-in-focus.
I picked up a K20 to shoot an event today and it went quite well... but not perfect.
setup: DA*50-135, shot at F3.2, 1/1000, whatever ISO required to reach those settings.
I went out the day before to dial in all the settings and try it out. I sat near the bottom of a hill that had a lot of cyclists coming down (~30mph) and tried to autofocus to capture them at close to full frame. The autofocus failed miserably. 10/10 failure rate. the Pentax AF is simply not fast enough to capture.
Catch in Focus - I set it up by trying to catch the cyclist in the perfect position using AF (which of course came out blurry). I then set the AF to AF.S and the lens to M. I pointed the camera at the next cyclist with the shutter release fully depressed and followed them all the way down the hill. 10/10 times the shutter released with the cyclist in perfect focus
During the event the cycling was nearly perfect... probably close to 95%. Ocassionally it would mis-fire when nothing in the frame was anywhere near in focus. Then I changed to another location and shot the run. I don't know if it had to do with the fact that the new location had the runners in full sun (running into the sun) but the catch-in-focus was <50%. After a bunch of failures I tested it out by depressing the shutter release halfway and watching for the in-focus "dot" to appear. That dot would frequently appear 3 different times at different distances (while the focus on the lens was not changing). I started to feel a little panicky thinking that the camera was going to let me down and ruin a whole section of the race so I tried switching to autofocus, figuring that the runners were going significantly slower than the cyclists so maybe it could keep up. For the most part the AF.C worked well with close to ~75% in perfect focus with another 10% just a little soft (but probably still OK).
There are a few reasons I can think why I may have been having a little trouble on the run.
1. the bouncing motion of the runners was somehow messing with the AF computer
2. The direct sunlight (lots of runners had white jerseys) caused a near blow-out situation and the AF may have had a tough time with it.
In the end everything worked out. The catch-in-focus was positively brilliant on the cycling while the AF.C seemed adequate for the run. Clearly Pentax has some room for improvement with their AF but for now (with only some minor adjustments to technique) everything seems to be working out.