I second Corey's caution to read the instructions and warnings that come with your pressure cooker. I have an electric pressure cooker and use it 4-5 times a week to prepare all manner of fare from beans and brown rice to stews and roasts.
One thing to be very careful about is not to fill your pressure cooker more than 2/3rds full so that there will be room for the pressure to build. Air can be compressed but liquid cannot. You will be cooking at about 248 degrees F. if your pressure cooker builds 15 psi of pressure. With an electric pressure cooker you don't have to worry about excess heat under your pot, but with a stovetop model you should be careful to cook at the lowest flame or power that will keep the pressure up. The food on the bottom of the pot can still burn if the flame is too high.
Be very careful with kids around a pressure cooker since the high heat and escaping steam can be hazards not present in regular stovetop cooking.
The pressure relief valve is a very important component of the pressure cooker. This valve can be clogged or fouled by foaming of certain types of foods (usually high protein foods). Foaming is common with beans, rice, pastas, etc. If the pressure relief valve is plugged the pressure could build to a dangerous level.
for a good source of pressure cooking information.
There are also some great recipies in this discussion forum for pressure cookers. Use the search function to look for "pressure cooker" or "pressure cooking".