How you work out is much more important than how much.
It's perfectly possible to do more in 20 minutes than what other people do in 3 hours. Lots of people at the gym are wasting their time.
Staying in good shape shouldn't take more than a half hour at a time, and it shouldn't require expensive equipment or gym memberships.
Here's a great video that demonstrates how to stay fit with 15 minutes a day.
Health Kismet Blog 