Define "okay." Cruise control has gotten "stuck" at 50mph[0], and electronic throttle control has left the throttle open disregarding user input[1].
So yeah, it's not some apocalyptic, universally-agreed failure that happens every day, but people have actually been killed[2] because the machine did something the driver wouldn't have done if they were in full control. (Maybe it's "compensated" for by deaths that were prevented by having cruise control -- I suppose we can't know for sure.)
