The book was supposed to be bigger than Infinite Jest (presumably in length and thematically). We'll know for sure on April 15, 2011, when Little, Brown finally publishes the posthumous novel from David Foster Wallace, who killed himself in 2008.
Publisher's Weekly reports that The Pale King is about a handful of IRS tax-return processors in the 1980s, which makes that April 15 publication date all the more fitting. Since Wallace's death, rumors have swirled as to just how much of the manuscript was complete. PW writes that Wallace's editor Michael Pietsch said that while the book was incomplete, "it is a surprisingly whole and satisfying reading experience."