I'll make this simple. A great book is a book that has rereadability. It's something that you may want to read more than once, and each time you read it again, you enjoy it just as much, if not more, with each successive reading.
In other words, like a fine wine, a great book never gets old, but just gets better with time. And great books are in my opinion more enjoyable reading in paper format. Paper is easier on the eyes, and there is perhaps a certain romantic quality about a traditional paper bound book, that will always make them more appealing to me than their digitized counterpart.
But an ebook may be a great format for a not so great book, and more suitable for lighter reading, supplemental reading, preview reading, and for reading on a budget, something that you use temporarily until you can afford to acquire the hardcover version for your permanent collection.
I like to collect free ebooks, to read, or skim through as I see fit. I don't have an actual ebook reader yet, but I use my netbook or my older, larger, dinosaur of a laptop, to read ebooks on. I've never purchased an ebook in my life, but whenever I can find them free online, I save them to my portable flash drive, which houses hundreds of titles in my virtual ebook library.
My ebook collection is primarily non-fiction. I cannot enjoy reading fictional stories in electronic format. There is just something that doesn't feel quite right about it to me. I am a romantic, and at least when it comes to reading literature, I much prefer the kinesthetic experience of hearing the crisp sounds of the turning of the pages and the feeling of the paper in my hands. I enjoy that especially if it's a great book, otherwise if not, it doesn't matter so much. It's just not quite the same reading online, or in electronic format. There is something dehumanizing about this virtual experience, this reading or interacting in electronic cyberspace. It has its place certainly, but when it comes to books, sometimes reading an actual book is a much richer and more satisfying experience than reading it online.
Of course there are benefits to ebooks, aside from their portability and relative low cost, one of the most noteworthy features is in the interactivity and multi-dimensionality of the medium, with hyperlinking, and fast as a speeding bullet information retrieval, where you have the ability to search an entire library for a single piece of information, whether that be a source or a specific quote, in a matter of minutes or seconds, something that could take you hours if you had to do it all by hand kinesthetically.
So if its purely information your after, which is most often the case when reading non-fiction, I have no problem reading it or previewing it on an e-book. But if it's a great book with rereadablity I'd much prefer reading its paper version. And especially if I'm reading classic literature, where speed or time is not a issue, and I just want to sit back and enjoy a leisurely read, nothing compares to holding and reading an actual paper bound book in my hands.
Anyways, most of my ebooks are non-fiction. The only exception to this rule would be when the fictional title may be out of print, or when I would have a hard time finding a hard copy of it, or if I simply want a quick preview of it for whatever reason. Then by all means if I can find it in ebook format, I'll take that over not being able to read it at all. Many of my ebooks are ones that I come across by chance, and similar to browsing a title in a library or a store, may warrant only a brief skimming or quick overview inspection of, and is not something to purchase and take home with you and explore more in depth.
But other ebooks I have that don't fall into this category, books that I would consider great and worthy of a place in my lifetime collection, are simply those that I can not currently afford or do not have the space to keep them. So these ebooks are temporary, a temporary means to a less temporary end. All ebooks, both good and bad, are temporary. In fact, all books are temporary. Just as all life is temporary. Paper deteriorates over time, as do our bodies deteriorate over time. Nothing lasts forever. But a good hard cover book printed on acid free paper, should at least last you a lifetime.
Whereas ebooks, and ebook readers, I think will not last as long. They are more ephemeral, and less dependable. If your electricity goes out, you're out of luck. So you can enjoy your ebooks while you can, use it as a tool to preview what's out there, but if you really love books, make sure to get a hard copy of your favorite books, the greatest books ever written, or anything with rereadability. Being the creme of the crop, the pinnacle of the peak, the best of the best, it will be something that will last you much longer, and that you'll never get tired of. In other words, it will be a worthwhile investment.