As a fulltime writer, I have several ebooks in the works, some of the frivolous variety.
All of it is stuff already written but I've never gotten around to publishing. Free/creative commons, etc.
That said, I think every halfway intelligent person has at least 3 good books in them. The key question is do you want to spend the time on it (given the lack of rewards and the other challenges that vie for your attention).
Another thing is what the audience is going to be like. The Audience for traditional novels is dwindling, but nonfiction is doing pretty well; so are technical books. Ebooks now make smaller forms more affordable for publication and more accessible.
I wrote a piece about the networked novel for teleread which might be relevant.
http://www.teleread.org/blog/?p=3905
Writing a book depends less on talent than motivation and the ability to set aside a certain block of time for it.