Readmill

 Readmill  was a silo for reading ebooks and making annotations. It is shutting down on 2014-07-01.

Exports
Exports are available from Readmill and produce files in various formats.

Their data export (requires login) outputs .zip archive with .txt .json .xml plus a bunch of assets.

Here is a sample of some of the annotation JSON (as noted in IRC 2014-03-29)

"highlights": [ {   "content": "The Journalist too, would not believe at any price, and joined the Editor in the easy work of heaping ridicule on the whole thing. They were both the new kind of journalist—very joyous, irreverent young men.", "position": 0.162775, "highlighted_at": "2013-06-27T10:51:37Z", "locators": { "pre": "lothes-brushes in the Future? ", "mid": "The Journalist too, would not believe at any price, and joined the Editor in the easy work of heaping ridicule on the whole thing. They were both the new kind of journalist—very joyous, irreverent young men.", "post": " 'Our Special Correspondent in", "position": 0.16277533769607544 },   "comments_count": 0, "comments": [], ... } ]