Benefits of mineral springs and thermal spas?

So, I went on a little getaway to a spa resort yesterday. I ended up chatting with this lovely older lady there who was raving about the whole experience. She told me she’s been hitting different spas all over the country for twenty years now. Apparently, it’s what keeps her going—she deals with some pretty bad arthritis and rheumatism, so these trips are basically her lifeline. She had this theory that things actually feel worse right before you start seeing the real benefits of the treatment. Anyway, it got me thinking. Does anyone here have much experience with spa therapy? I'd love to hear your stories, and since the mineral content varies so much from one place to another, does anyone know which US resorts are actually the most effective for healing?

Any kind of movement in water—or better yet, the ocean—is fundamentally natural and incredibly beneficial.
It’s actually our most primal state, much like how an unborn baby moves in the womb... just pure, fluid motion.
It works more muscles and joints than almost anything else, which is why I'd recommend it to everyone—especially those dealing with physical limitations or mobility issues.

The real question is which spa and what kind of thermal water we're talking about? Because one size definitely doesn't fit all when it comes to mineral water. It all depends on what you're actually dealing with—the specific issue, the pain, or whatever ailment you've got...

The site www.toplice.com has a pretty decent comparison of various spas across the US.
I guess I'm not sure how reliable the data is, but it’s probably a good starting point for further research.