I make heavy use of books and a large database (4.75 million games), as I see those as being integral to correspondence chess. I personally feel that correspondence play is the best form of the game, and I had the good fortune of studying with the late Anton Sildmets, a winner of the Golden Knights Tournament (effectively the correspondence championship of the United States), when I was a teenager. Now at age 80, I think that correspondence play is helping me ward off Alzheimer's Disease -- at least I sincerely hope so! I try to move a couple of times per day, but in a "difficult" position I will often use the full time allowed for analysis.