On Joe Konrath's blog, he posts some hard numbers (scroll down a bit to see this):

Here are my latest royalty statement figures for my six Hyperion titles and my Hachette title, for Jan 1 - June 30, 2011. Paper sales are hardcover and mass market combined.

Whiskey Sour paper sales: $1450.00
Whiskey Sour ebook sales: $5395.00

Bloody Mary paper sales: $463.00
Bloody Mary ebook sales: $2591.00

Rusty Nail paper sales: $226.00
Rusty Nail ebook sales: $3220.00

Dirty Martini paper sales: $415.00
Dirty Martini ebook sales: $3370.00

Fuzzy Navel paper sales: $485.00
Fuzzy Navel ebook sales: $3110.00

Cherry Bomb paper sales: $224.00
Cherry Bomb ebook sales: $3864.00

Afraid paper sales: $1608.00
Afraid ebook sales: $12,158.00

WOW. Well, that pretty much sums up where things are headed, doesn't it?