There are three types of ebooks: the first are web books which can easily be accessed via the internet. The second are palm books which are more portable and internet connection is not required. The third type are produced with electronic ink to display content that uses lucent technologies.
The major advantage though is the method of publication. Electronic books can be created by anyone and have the potential to spread worldwide. As a result they can be accessed from any location virtually without the damage that this can cause to a printed copy. Online catalogues are used now by most libraries and reader can store thousands of books in a tiny space, accesible via the cloud at any point in time.
ebook proponants also cite the disadvantages of paper copies; these are mainly space, weight and cost.
However on the side of the printed copy; the method of printing books on paper has a long history behind it. Printed communication has been found in many mediums, from cave paintings, through clay tablets and wooden blocks and through Gutenberg's press to moveable type. There are several unique advantages that the traditional printed publications offer.
Books don't suffer from light/glare issues and eye strain that continually staring at a screen can bring. Books come in all shapes and sizes, with photos, illustrations, silky pages and textured papers that appeal to many readers. Books are ready the moment that you pick them up and you can work easily with many books at once. They can be shared, resold and can be perused freely in stores before purchase. They can withstand quite a lot of usage and some last for centuries. No batteries required.
Certain qualities of print will not be matched by electronic devices within the foreseeable future and the virtual aspects of electronic information are sometimes difficult for readers to comprehend than the structure of a paperbound book.
For my part I find that for going on holiday and not having to carry a suitcase load of books is extremely useful, however I still love the feeling of a 'proper' book and bedtime reading wouldn't be the same without them.