If you want to get in serious shape, do some inline speed skating.
I do skateboard myself, but mostly in skateparks.
Marathon style rollerblade(with an IPOD

) is my exercise of choice for cardio/endurance workout. It's about 100 times more fun than jogging.
A lot say that inline speed skating is more technical than cyclism.
Here's the 2 BONT models I'm considering buying because I'm currently riding some street/ramp rollerblades with 50mm wheels which is really ineffective(They are the 2 newbie/intermediate models)
Alpha 90mm 250$ (Recreational)
Semi-Race 100mm 400$
Check out
http://www.bont.com for more infos.