I think the point of frameworks like Genesis or Thesis is that they help create a wide variety of site layouts and themes without having to re-code core features every time. I know some people who are expert developers who still use frameworks to speed up their theme development. And they're a godsend for people who want to develop a variety of full-featured sites but who don't know HTML/CSS and don't want to be beholden to a designer or developer for every little change they want to make to the site layout.
Personally, up until now my M.O. had been to find a theme I like and tweak it to suit myself. It's easier than starting from scratch every time, and I don't run into the constraints that a framework will inevitably build in to the process.
So, sorry, Lisa, I don't have any personal experience with Genesis to report.
That said, I've been thinking of experimenting with frameworks, because I have a LOT of sites under my care, and I'm thinking that employing a framework might be a handy way to keep their themes visually "current" with less hassle. But I'm a cheapskate, so I'm wary of locking myself in with a paid framework, only to find out it's not "The One." My feeling is, by starting with a free framework, I can experiment and see if the paradigm works for me without spending any cash out of pocket. (We cheapskates hate spending cash out of pocket. )
Lisa, if you're interested in frameworks but not sure if you want to spend money for one right now (and maybe not ever...) you might find this article on frameworks from the WordPress Codex helpful, as well as this review of seven free frameworks posted at WPMU.org.