I woke up in the middle of the night and realized that I'd not plopped enough vias around voltage regulator U5. It's weird that my brain works that way, checking things in background. Unfortunately, the boards are already ordered.
It's a SOT223 and might dissipate three watts. Each via could be roughly 30K/W but they aren't strictly in parallel, and all land nearby on the layer 2 ground pour, which will be a hot spot. I should have made the topside patch bigger and had more vias. Or helped the regulator with some resistors or something.
I guess I could have production fill the vias with solder; that would cool the regulator a little.
Gotta go to Molly Stones now. They do a dynamite corned beef and cabbage on St Patricks Day. One bad thing about this town is its scarcity of decent corned beef.