Data point:
1K flying on mileage ticket (13.5K) STL-IAH-SAT on 6/26/25. 6 hour delay from STL due to fuel leaking from wing that could not be easily fixed. United had to fly in replacement airplane in from IAH. No other itineraries were available except via Denver much later in the day which hindsight being 20/20 may have been a better move. After takeoff (probably irrelevant to compensation): diverted to LIT for thunderstorms at IAH, followed by minor pandemonium in Houston upon eventual arrival as they were working hard to dig out from hours of ramp closure. Ultimately arrived SAT about 12 hours after scheduled arrival.
No meal vouchers proactively offered, although when I requested via chat I got $40.
No email or card handed out referring to Customer Appreciation website but I input my data there and was offered $150 or 7.5K miles.
-z