The world's largest book publisher of tech books, O'Reilly, stopped using DRM on its books 18 months ago. Since then it's seen it's own sales of eBooks increase by 104%. When you think of DRM and tech books you might think "Wouldn't these types of people be copying these books and not be paying? They all seem to crack every other bit of software out there."
Seems like that theory is true.
If you look at US wholesale eBook sales from Q1-Q3 of 2009 you'll see that sales have increased nearly 200% compared to Q1 - Q3 of 2008 according to IDPF. O'Reilly is well behind the industry trend here.
It looks like DRM vendors will now have some useful information at their hands to show that without DRM you'll likely lose out on sales due to copied books.
Now, I'd just like to point out how even though all these figures by themselves are true, it is all how you put them together to tell the story that then creates mis-information. Someone else may look at these figures and say that O'Reilly eBook Revenue is up 104% if you compare their numbers from the year prior. Well that's what O'Reilly did. And then Boing Boing decided to write about what they said and before you know it people start believing what is told without questioning it.
If you have enough figures, you can tell any story you want.