Regarding running surfaces....
From
www.runnersworld.com
Pros: Sand gives an opportunity to run barefoot in an pleasant environment. Running through dunes provides good resistance training and strengthens the legs.
Cons: Despite being great for building leg strength, the softness of the sand means a higher risk of Achilles tendon injury. Also, though the sand is firmer at the water’s edge [assuming you run at the beach], the tilt of the surface puts uneven stresses on the body. And while it’s tempting to run barefoot, watch out for blisters.
Personally, I prefer running on asphalt & concrete. Interestingly, concrete got one of the lowest ratings b/c of the shock on the body it causes.
Here's the article I cited about running surfaces
http://www.runnersworld.co.uk/news/article.asp?UAN=152
Seniors this Sunday! errr kill.