In the central sections of Barcelona I'd say about 40% of the time I take the metro (L5), it's too overcrowded with people to have a normal, comfortable ride. Right now I'm surrounded by way too many people with only centimeters or less of personal space. I don't remember it being this consistently overcrowded years ago.
Edit: I should indicate that I take the metro at least twice every day, but outside of normal peak hours. It's almost guaranteed overstuffed with people around 20.30-21.30, and often quite full around 14.30-15.30. In the morning around 10:30-12:30 is usually not so bad at all.
How about in your city?