From Critical Mass:

    Not officially announced yet, but insiders know, and tell Critical Mass, “It’s official. The last issue of Book World in print will be the February 15, 2009 issue. Thereafter, content will be split between the Outlook section and Style & Arts on Sundays. Daily book reviews in Style will continue. The promise is that there will be four additional broadsheet pages in Outlook for book coverage and one additional page in Style & Arts. That’s an equivalent of 12 tabloid pages. (Book World is 16 pages.) Jonathan Yardley’s reviews will appear in Outlook. Michael Dirda’s will appear in Style. The staff of Book World will be kept together under the editorship of Rachel Shea.

And the NYT confirms.

Book reviews will continue online.