Now let's get from great PR messages from Vitalsource back to the reality.

.VBK ebooks can be opened with Vitalsource Bookshelf software. You you get three-way access to your books:

• download VBK ebooks and open them on your computer with Vitalsource Bookshelf software (Windows, Mac OS);
• online,
• mobile (Apple iPad, Apple iPod, Apple iPhone).

The good thing is that notes and highlights automatically stay in sync no matter where you make them.

The bad things about VBK file format:

• DRM protection, so you can potentially lose legally purchased content anytime (due to computer/HDD crash, ebook content-provider getting out of business,...)
  
  You can print VBK ebooks, so use a virtual PDF printer like PDFCreator, doPDF,... for backing up your ebooks in PDF format.
• eBook Readers don't support VBK format, and since VBK books are DRM protected you can't convert them to Amazon Kindle, Sony Reader, Nook,...
• No Linux support
• No Android support.