Now there are two reasons for this.
One is just the environment. The events are taking place between 9:00am and 5:00pm. It's August. It's California. The light is bright and harsh. Not much one can do about that.
The other is a bit of stupidity. I decided to shoot using a shutter-priority AE mode, with a high shutter speed to guarantee that I could stop the action. Sounds good, no? No. I've got under 2 stops of exposure latitude in the lens when it's racked out (f/3.5-f/8). I should have gone with the aperture-priority AE mode, set a wide-ish aperture (say f/4) which would have still forced the high shutter speeds I wanted, but given the AE a bit more latitude.
What else did I learn?
Well, it was reinforced to me why I want to upgrade to a dSLR.
I want something with more exposure latitude in the lens, 4 stops would be nice. I want a lens I can open out far enough to blur out the background. I can get both for a reasonable price in a 50mm prime (which makes a good long-ish lens for portrait shooting on an APS-C or DX format camera).
I want a zoom that I can just grab and change, not something servo-driven.
I want faster (smarter) and more accurate AF and AE.
I want less shutter lag.
I want off-camera flash.
After spending a few hours at Keeble & Shuchat on Saturday, it's down to (probably, I'll have to wait until the production models deliver and see what they're really like) the Canon EOS 50D or the Nikon D90. The 40D and the D80 (which are very close in form-factor to the upcoming models) were both pretty comfortable to hold and use. The Rebel XSi just doesn't fit in my hands. The Olympus E-520 and E-3 are interesting (and the E-520 would be a relative bargain) and the Olympus Digital Zuiko lenses are really nice, but I've got to think about whether or not I'm willing to give up the option of the really fast primes available for the other brands.