There is a lot of confusion out there about what constitutes a digital book or magazine. Some references are even to websites that call themselves magazines. And I'm not going to slam that idea - if it gets them more hits, and they gain an audience for their information, great. But for myself, when I find one of those, I'm frequently disappointed as I hoped for a less website-y and instead more visual presentation.
In this post I'm going to sift through the muddy waters a bit and give the picture I see of what's available to writers and publishers of content right now. I'll put in my two cents on what I think are the pros and cons of the options and at the end, let you know how we can help with any of these options should you need consulting, design or implementation.
Let's start with the most basic - a PDF document. Everyone knows about PDF because thankfully, it's become a standard for sending things to press. I love PDF because I remember before there WAS PDF and designers had to do way more packaging and worrying over print issues. PDF format is a wonderful thing. And yes, you can use this format to easily post on the web any and all of your documents. These can be viewed in some browsers, sometimes without download, but most frequently, when a viewer clicks on your PDF link, they will be required to download the document to their hard drive. The term "e-book" seems to often be used for long pdf documents that are available for purchase (or free) on individual's websites. It's one format for self-publishing, but it has the drawback of typically not having much security in terms of digital rights management and is freely passed around.
One of the main drawback of a PDF is this downloading of a file. (You also have to download Acrobat Reader, but that is so standard on computers today, that I wouldn't be too concerned about that.) Depending on the size of your document, that download can be a deal breaker. It can take a while. It's one more thing for a viewer to deal with unless you have a reader ready and wanting to retain a large digital file. If you include lots of images or rich media (yes, PDFs can contain media if you work it right) the file gets very large very fast. But for small documents, this is a nice, easy, do-it-yourself method of putting up content on your site. Great for forms (if you don't have e-commerce or a database and would like someone to fax or mail you information), small brochures, boring legal paperwork. As much as I hate paper, I'm happy our school puts up a nice visual yearly calendar in pdf form that I can print out and stick on the frig.
For large, visual, and rich media enhanced magazines or books, I whole-heartedly endorse Flash page flip conversion (from the likely large PDF files that come with these more complex documents.) Not only do I love this 
format because it's our specialty, but also because this is an easy way to convert beautiful visual print assets into immediate digital assets that will retain the original design. Then you can enhance them easily with media while you're at it. Flash editions usually come with the ability to apply a strict Digital Rights Management environment if you want security with your document - either for selling, for tracking subscribers or for limiting the audience. Many of them can be created with a company that can offer an e-commerce solution as well should you want to sell your book or magazine.
Flash versions are good for handling media such as video, animations and audio within a format that looks like a magazine layout. In fact, the ability to lay out the content in standard page layout software can also be a boon with quickly designing anything for online viewing - you can create a great looking newsletter or digital brochure without learning web design or html. The Flash conversion hands you a simple url link that you can post on your website or in an email. The viewer clicks the link and boom, gets a whole reading experience right in the browser with no downloads required.
One con to Flash editions are that these are not yet viewable on e-readers such as the Kindle or iPhone. And that brings us to the last format, e-books.
"E-book" is starting to most commonly refer to file formats that are available for the new readers such as Kindle, Sony's Reader or the Nook. With the e-book format, you have the upside of getting quickly into the commercial mainstream with your content - for example, you can upload e-books directly to Amazon by using some of their partnering options. However, that content will need to be almost completely text as these readers are very limited in their ability to show any pictures or video, if showing them at all. A further setback for some publishers is that E-book formatting is itself an art form and comes with a learning curve if you want the chapters of your book and a Table of Contents to work well.
Thanks for reading! We welcome any comments about other formats or opinions on digital formats here. And please keep us in mind - CatStone Press is ready to help with any of these new digital formats, depending on the needs of your business or publication. Our design services are available for creating publications and documents from scratch or for helping you tweak your own documents to fit your desired format. Whether you'd just like help posting a PDF, want to make your magazine soar on the web, or would like help formatting your next e-novel, we're ready to help with your transition from paper to digital.