That's a good thought, I didn't consider that. However, the chain and cassette are all relatively new, with each having about 250 miles of wear. At any rate, I just checked the chain for stretch and measured no perceptible stretch, and I didn't notice any wear on the 30t cog.

We're going on a ride this morning, and I'll continue to play with the derailleur adjustment--maybe I simply missed something in my adjustments of the barrel adjuster, limit screws, etc. Knowing my mechanical skills, it's most likely a user error issue :-)