I found this interesting information regarding ebook sales – a definite trend here.

Got this via @namenick on Twitter, who in turn, got it from Infographic

Note that 2010 and 2011 figures are estimated, but on good data. All data is based on reports from 14 top publishers, to the Association of American Publishers.

Year	US$M
2002	5.7
2003	7.3
2004	9.5
2005	10.6
2006	20.0
2007	31.8
2008	44.5
2009	165.8
2010	439.2
2011	724.2