We’ve discussed the KDP select experience before, but here is a more recent post at the www.epublishabook.com blog, by author Kirkus MacGowan:

I searched the internet for information about KDPSelect. Not about the program itself, but about how things work, or about any author’s particular experience. I’d heard rave reviews and I’d heard others who say they barely gave a book away.

Kirkus lists his concerns, providing some numbers for what constitutes a bestseller in various categories, and set down to promote his book:

I promoted my giveaway 4-5 days before my book was free on the KDP Select program. This explains why I went from a 30K rank down to about 190K in one week. Everybody knew my book would be free!
The night before, I climbed into bed wondering which group my book would fit into the next day. Would it rocket up the Amazon free bestseller list? Would I even come close?

Read about the results of his experiment here: http://www.epublishabook.com/2012/04/09/my-experience-with-kdp-select