I'd say it is way too little in some cases, unless you can psychically be assured that the ebook will sell many copies. And while lower price / supply and demand may encourage that, I wouldn't be certain that's always sufficiently the case.
I can't help but think of Stephen R. Donaldson in this discussion -- his General Interview on his website touches on ebooks, publishing and author's rights several times, and it fairly well boils down to "As long as I receive a reasonable remuneration for my work, things are fine."
And here's the catch -- it is pretty obvious to me (as very much a non-writer), that it is a serious level of work. And as such, I'm more than willing to pay a reasonable price as compensation. $9.99 for all his books (given he's more than a little of an acquired taste and unfortunately doesn't seem likely to build a huge new readership)? Unlikely to be enough unless we could ensure that money went mostly directly to him. So -- in the same way I prefer acquiring his work in hardback to both get a product that lasts better through multiple reads and to knowingly pay the "early adopter" fees that funnel more money his way than el-cheapo paperback editions, I would pay more for an e-book as a support mechanism.
I'm sure others have similar niche or less popular authors, or can cite other examples such as more limited interest books (some of the more arcane history texts probably fall into this category).
Back more on-topic, there's no way I'm ever buying a serious book with anything jumping, wiggling, flashing or spamming me. Nor do I want a book which requires a net connection to update or check anything. Probably why I have no interest in an ebook reader in the first place.