So far I'm 50% overall on CPU-eligible flights this year. 40% success rate during peak hours and 60% success rate during off-peak hours, based on an admittedly subjective definition of peak.

I got one of those CPUs when a flight was delayed by five hours. Made the whole thing a lot less miserable. Maybe that's one tweak that UA can make. Be a bit more generous with CPUs during anticipated ATC delays, and maybe sell a few more TODs when the sky is blue.