I definitely ask my DP if he noticed anything, either in my performance or someone else's.
Even when I'm on camera and acting, half my brain is devoted to just watching the other actor and seeing what they're doing.
I guess it comes down to, I know what I want my character to be and I can tell when I didn't give the line reading I wanted.
It's a juggling act, but if you make sure that YOU are the most prepared person on set, it allows you to focus on other actors.
Also, I think I give the more interesting roles to co-stars, where as my character (Ryan) is the straight man. So the co-stars have the harder jobs! lol