Depends on the game. If it's not really demanding on reaction time, and the game is locked framerate I'm fine with 30, like Okami. However if the game is not locked FPS and I still can't hit 60 FPS at least on my 1440p monitor I'd probably just play something else (because I know I could have better experience is I could run it).
However for shooter and reaction heavy games I always aim to max out my 144 Hz monitor, even 60 FPS can feel sluggish for me