Skateboards are for doing tricks such as ollies(jumping), grinds, and flips. It is not ideal for rolling on anything other than smooth ground, and they are typically used in purpose built skateparks and urban street obstacles such as stairs, ledges and handrails.

Longboards are for rolling on roads and pathways in parks. There are many disciplines such as recreational cruising and transportation, to more serious styles such as aggresive freeriding and competitive downhill racing. It is more a sport based on rolling and sliding, and not so much on typical skateboardong tricks.

They may look alike but they are quite different and are for different purposes.

SKATEboarding typically appeals to male teenagers and young adults who enjoy the challenge of learning millions of tricks and doing them off bigger and bigger obstacles to a point where they can do said tricks down handrails and 10+ stairs. It is an extremely difficult sport for most people.

Longboarding is a much more "open" sport, with participants from many different age groups and backgrounds due to the many different disciplines and less emphasis on high impact tricks. There are styles of longboarding suitable for the most casual user to the most serious racer.

For detailed information on longboarding, check out our 101/FAQ here
http://www.loveskatepark.com/forum/viewtopic.php?f=9&t=1053