Not written from my own experience, alas.
I just ran across a blog post by Vampire romance author Lynn Viehl http://www.genreality.net/the-reality-of-a-times-bestseller
Her novel "Twilight Falls" (sixth in a series) just hit #19 on the NYT bestseller list. It is some indication of the importance that the list holds in my reading life, I believe, that I have neither read Ms. Viehl's books nor heard of her before. This is certainly not intended to be a reflection on her work, just that my reading tastes tend to go in other directions. That said, I appreciate the honesty of her posting about the actual financials involved, though I have to admit it's pretty depressing as well.
In my writing life, things look a bit different. Like most other small press authors, I tended to fantasize that in the unlikely event any of my current (or quite possibly, future) books made it to the glorious heights of the NYT list, I would actually make enough to come close to replacing my day job with, you know, writing. It's the Holy Grail that most writers dream of but very few achieve. The fact that it's so rarely demystified for those of outside bestsellerdom is linked to that dream - who'd want to admit that they're still can't afford the gold Rolls Royce after they've hit the writing pinnacle, after all?
Of course, I'm guessing that if she gets a movie deal, the numbers go up a bit. I hope she posts about that as well if it happens. Now to go back to speculating on what Clancy's numbers look like, pre-movie deals.
Causes Catherine Lundoff Supports
The Women's Prison Book Project - provides books to incarcerated women Theater Unbound - promotes theater by women: playwrights, directors, performers...