The UK mass-market paperback edition of The Way of Kings has been split in half due to the book's extreme length. Part 1 will be published on 26 May 2011, followed by Part 2 on 16 June. The American paperback, in one volume (of 1,344 pages!) will hit on 24 May.
In related news, the UK gets its own versions of Elantris on 11 August, The Alloy of Law on 17 November and Warbreaker in December.