At first, BB tanks look incredibly sterile and unnatural. After a few months, though, coralline algae takes hold and the bottom looks like the back of the tank. I even have anthelia growing on the bottom of my 120g, and some spoge growing under some rockwork.
I would never go back to using a sandbed. The amount of crud siphoned from our BB systems on a weekly basis would make you seriously think twice about a sandbed and how much crud actually accumulates there. Even the animals in the sandbed that eat crud, end up making crud of their own.
Here's my page on maintaining BB, sumpless, skimmerless systems. Skip all the text, if you want. All you really need to see are the pics of the changewater pails near the bottom of the page....
http://www.lostmymarblz.com/reeftips...ottomtanks.htm