I purchased my iPad in hopes of replacing all my technical print books with ebook versions so I could carry them around with me between home and work. I hated leaving a book behind, since I might need it at the other location--which happened just the other day; I needed my Programing Perl book, and there it was on my iPad. I also was tired of having so many books in my bookcase, since I was moving a lot. Twice in one year, both on very hot days. 'Nuff said.
So what have my results been? I'd have to say very good. I have been able to replace 5 of the 8 books I wanted to replace. There were a few others that would have been nice to replace, but since they were so old anyway, it wasn't a big deal. The ones I have replaced are Programming Perl (ePub), Java Swing (PDF), Programming Game AI by Example (Kindle), Open GL Super Bible (Kindle), Cocoa Programming for Mac OS X (Kindle).
I'm really glad O'Reilly is one of my favorite publishers. They have by far the best ebook policy. You won't find their ebooks on Amazon. Instead they offer them for sale on their own site. This is a great thing since I am able to purchase the book and read it as PDF, Kindle or my preferred format, ePub. All formats are DRM free, and not watermarked. They have great prices and great deals. I was able to purchase 6 new ebooks from them for $65 with their buy 3 get 3 free deal (exclusive membership offer for ebooks). They will also sell you upgrades from print versions of books you own for $5. You can't beat that. $65 is only about $10 more then I would pay for a single book, and I got 6 of them! I have found other publishers doing similar, but with mixed results. One publisher only offered PDF watermarked ebooks. Others were only available on Amazon as Kindle ebooks.
While O'Reilly offers Kindle versions, it should be noted that I have not been able to transfer those DRM free Kindle books (like the ones from O'Reilly) onto my iPad. If you had a Kindle device, you could just transfer it via Amazon's paid transfer service, or when you hook it up via usb. It appears that if you want them on your Kindle app, you will have to purchase the ebook from Amazon. So for the iPad, choose ePub or PDF.
For novels, I'll admit only had a couple Stephen King books since I tossed all the others. I had made my mind up to only get ePub novels, but now I am starting to lean towards Kindle. The selection is so much bigger; I recently purchased Dean Koontz Phantoms from Amazon which is not yet available on the iBookstore, while some other Koontz titles are. And with the recent fall in price of the Kindle device, it isn't out of the realm of possibility that I would get one for the wife. So let's see. $140 (cost of a Kindle) is about the price of a nice book case. A bookcase can hold about 100, maybe 200 if you pack them in. A Kindle will hold up to 3,500 books. That means the Kindle will replace 17 bookcases! I'd have to say it is much cheaper in the long run to buy a Kindle. See how that works? With the right mindset, you can justify just about any technical gadget.
After using both the Kindle app and the iBooks app, on both the iPad and iPhone, I prefer the iBooks app. For technical books, I like being able to use more then one-highlight color. For example, I use yellow as my main highlight color to highlight important things I will refer to often. Blue is for minor highlights, like the important parts of a series of steps describing how to modify some source code, or editing a photograph. Finally, pink is used to mark errata, corrections to the book since it was published. I also like that the entire screen is used to show your bookmarks and highlights on the iPad. The Kindle app sticks you with this tiny window at the bottom of the screen. The iPhone Kindle app is a little better in that it uses the entire screen. For novels, while I prefer iBooks, I think I will be switching to Kindle ebooks because of the selection, and since I am thinking of getting a Kindle reader.
When it comes to reading PDF ebooks and documents, I turn to iAnnotate PDF. While it isn't as pretty as using iBooks, it is much more functional. I can highlight text, add bookmarks, add comments, and even draw on the document. It has become my favorite way to mark up other people’s stories. I can email an annotation summary along with the marked up document, or save the document back to Dropbox when I am ready to share the comments I made.
Over all, I prefer using one reader for everything, but I'm okay with switching between them. As time goes on, I hope we will end up with a standard format so I can use just one reader. But until then, I have my 3 favorites.