Lots of talk about these lately for certain. I run a dsb and love it, full of life and after a few years no signs of any trouble at all in the way of ate, ites, nh3, etc. I personally think they add a great dimension to the tank in contrast to the bare bottom tanks. CC is clearly not preferred as i can lead to nitrate problems. You need a dsb of 3-5 inches. I use 4 personally.
Dont get the ls at the store its a waste of money but do get a cup to seed ur bed from a bud, or if the lfs has a ls tank then go for it. You dont need the bacteria (will grow on its own) but u do want the critters. You can also get a det. kit which will cover ur needs.
pros:
done correctly can be an excellent filter to keep water under control and add biodiversity to your tank. no mantainece at all (shouldn't be disturbed.
cons:
not cheap unless u can get southdown playsand. Using CC can cause it to create nitrates (if your going to do it, do it right the first time and get the argonite).