Every so often Vook will put some of their titles on sale or even give them away for free. Right now you can get 5 titles. Actually, if you don't mind giving up all the enhancements, you can get a few dozen titles for free. but I don't know why you'd bother.
The enhancements only work in the iOS apps, so if you have an iGadget then you should get these free apps.
via Mike Cane
P.S. You can find other free Vook apps in ITunes. Just search for Vook.