From their press release:
E-book sales momentum was considerable (up 88% compared to Q1 2010), accounting for approximately 22% of revenue in the United States and 5% in the United Kingdom. This development is the result of very brisk sales of e-book readers at the end of the year. …
e-book sales will continue to grow in the United States, albeit at a less upbeat rate than in the first quarter, to reach 15% to 20% of revenues. E-books could account for 5% to 10% of revenues in the United Kingdom in 2011.
