The DCCD on my Type R has 6 settings. The dealer I bought mine from said to use 1 for everyday dry use, 2 if its wet and 3 in heavy rain or snow/gravel.

What settings does everyone else use and why?

 

It does not have 6 settings, there are 6 indicators on the dash (so you know roughly where you are) The adjustability goes beyond 6 settings. Read this extremely helpful thread from John Felstead, and all will become apparent!
http://bbs.scoobynet.co.uk/showthread.php?t=143750