BytaFont v1.5 has been released and is available on ModMyi repository.

You are now allowed to change the font used by iBooks, via an additional option provided within the More tab.
Be sure you have Georgia selected as your iBooks font, otherwise you won’t see it.

If you get the following error when you apply a font, it means that the font needs to be updated because the files necessary for skinning iBooks are missing; just let us know and we’ll give priority to the font for the update.

We are updating all the existing fonts but it will take some time, so please be patient.
In the meanwhile, you can find all the iOS 5 complete fonts at http://www.iphoneruler.net/tag/ios-5

You can find more info about how to use BytaFont at BytaFont v1.5 overview.