I agree with mumshquat (although he was a little harsh). Shocks are really are an important part of a car that handles well. I think 50,000 miles sounds about right. Don't wait until they start leaking....some shocks never leak after 200,000 miles.
You can tell if a cars shocks are worn out by how much the body rolls. Especially under braking (the rear end rises up) or accelleration (front end rises up). Even cornering you can see a large gap between the tire and the wheel well. But shocks wear very slowly over time and sometimes it's hard to tell when they're worn out. You might have to have someone else drive the car so you can follow behind and watch for yourself.
It used to be that you could just push on a front or rear fender and bounce the car. If it kept bouncing, you needed new shocks. But this doesn't seem to apply as much anymore (unless your shocks are TOTALLY shot!).
Good shocks (Mazdaspeed, Tokiko, KYB, Bilstein, Koni) make a HUGE difference in the way your car handles. It will be much more predictable and the tires will stay in better contact with the road which means better traction.
I would look at this as a blessing. Now you have an excuse to buy a good set of Tokikos and make an improvement to your car. They aren't cheap (especially if you go for the adjustable versions), but you will be really happy with them. Later, if you decide to lower your car or add stiffer springs, you'll already have the upgraded shocks to match them.
