Well, now your chances for hitting the list with a paperback have more than doubled. Starting with the bestseller lists September 23, the NYT will split their paperback fiction list into two separate lists, one for mass-market and one for trade paperback (the bigger paperbacks). Each list will include the top 20 books, instead of just the top 15, for a total of 40 books that can now can themselves New York Times bestseller. The extended list of paperback fiction bestsellers, which includes "also selling" books is now 35 books long for each list.
Making the list is huge for authors, and I don't think the fact that is has expanded will discount that fact much.
The downside is that the lists take up an extra page, and right now that is going to come out of pages where reviews used to run.
What's the reason behind the change? Insiders say it will bring NYT more ads, because publishers want to buy a spot right next to the lists. And in general, publishers will probably buy more ads in any day's NYT's book pages when their titles are New York Times best sellers.