50 yards - or 50 meters, depending on your pool...

I count meters, not laps. For some reason, I find it easier and more meaningful (plus: I'm usually swimming with a goal, e.g. 1000 m, more than a time goal... or I renegotiate my goal as I go, like yesterday: ok I have 5 more minutes to go before it's half an hour, I can do 150 or 200 more meters...).