So 88% of sales are coming from ebooks, but I'm going to add a caveat. That 88% is only for sales through O'Reilly.com, their website. It doesn't include retail partners like college bookstores, B&N, and others.
I'm not surprised the website is showing such a larger chunk of ebook sales. Part of the reason you visit their site is to get the book as fast as possible, and getting an ebook in a minute will always trump getting a paper book in a couple days.
And in other news, they're also reporting that PDF use is declining. Four years ago it was PDF or paper, and now that O'Reilly offer Epub, Mobi, and other formats everyone has largely stopped using PDF.