People often say they don't have time as an excuse to do cafe sketches. Once I committed myself to do sketches everyday, I try to bring out my tiny sketchbook and pen, even I only have one min.
I used to draw at subway, trains, cafe and restaurant, now I've extended it to at the airport pickup (in the car), bank, medical center... even at um..... my.... great-grandma's..... funeral...
Well I know these weren't the BEST place to do sketches:
bank = unless you know they are robbering
in the car = esp. you are in the driver's seat! I parked on the roadside though
funeral = not really appropriate...
Of course, the bottomline is safety.
If you do quick gestures or draw in a tiny sketchbook (my current one is 4"x6", super tiny), you can always do them in a couple of minutes. Squeezing these couple of minutes can fill up your sketchbook in no time! Also, don't just carry the book with you, you have to open it and use it!
The more you draw, the faster you improve, the more you see around you.
I guess the only excuse I find is I'm too lazy to scan and put them online... hahaha... I still need to work on that... =P