I'll put my vote in for total immersion. I've used both the book and video mentioned, and they were helpful. Then I signed up for a weekend workshop, but it fell through. So instead, I got with a total immersion coach (they were listed on the website, and he was going to be involved with the workshop) for some private lessons, and that has helped more than anything. I spent 6 months retooling my stroke, only doing drills. I swam competitively in high school, but swimming has changed since then. It's about technique, not power.