The single best thing I've gotten from Lean Startup is the concept of doing an MVP. I released AR's (a functional demo of the core interaction -- it rings your phone and talks to you, then echoes your input onto your browser, that is it) about six months ago, after about two weeks or so of hacking on Twilio. That is close to my best spent two weeks ever from a learning perspective, since people have spent six months telling me "Yes, THIS, I want THIS." I thought AR was a good idea, and the people I talked to certainly had a raft of appointment/scheduling problems, but even a one-screen crystallization of my vision for the solution helped me move it from "something people might theoretically be interested in" to "something I have a high degree of confidence will sell."

If I had spent the last six months getting no emails about it, no signups in the post-demo form, and whatnot, I would probably have reevaluated whether AR was really what I wanted to be doing next, prior to spending a month writing real code for it.

Talk to customers, though -- if you need to call it Lean or not call it Lean to talk to customers, whatever, just do it.