Yes, the ability to search the book is clearly an adventage. I have lots of books on PDF in my computer and it is nice when you can do a word search across all of them. Can't do that with real books, where you are limited to indexes.
As far as the iPad goes, meh...I guess I am just not part of the target audience, I have everything I need with my MacBook Pro 15" (portability + power) and I also have an iPhone. so I really have no use for it.
As far as HTML5 vs Flash goes, sites like YouTube, Vimeo and other have already employed the HTML5 video tag and so you won't miss much unless you go to sites done entirely in Flash with no HTML version as a fallback (sloopy web designers do that). Adobe has very much failed to deliver a working Flash player for mobile devices and I think they have already lost the oportunity to capture the market. It is only a matter of time for HTML5 to capture the web video market.