Yes. It's very interesting and often difficult. I'm trying to write a book right now about the Kindle Fire, but I don't have one. It's hard to guess if, for instance, users without Wi-Fi access will be able to download apps from the Appstore and then transfer them to the Kindle FIre via uSB, how Mail is going to work, and what kind of browser it'll have. For instance, although I'm pretty sure there won't be an Netflix app, can users use Silk to go to Netflix.com and stream it? I just don't know how locked down it'll be.
As far as writing about the iPad, well, the next book is already partially written since the iPad 3 will be a superset of the iPad 2, plus all of the cool new iOS5 stuff. But what will be new?
I do a LOT of guessing and a lot of research :-).