I've been a paying subscriber for a few months. It's hit and miss. The value you get really depends on how well the information lines up with your particular business model.
A lot of the courses feel more like product demos ("here's the hard way to do it, or you could just sign up for my service, look how easy it is"). Not that they're worthless, but it's hard to give impartial advice and pitch your product at the same time.
(And you can't really expect people to just give away their best secrets. The best tricks are the ones that would stop working if everyone was doing it...)
That said, a few of the courses have inspired me to explore ideas I would have otherwise dismissed, and some of those ideas have worked out pretty well. Ultimately, $25/month is not a lot, if I bring in one extra sale, I've made a profit.
I've been consuming the free interviews for about a year and subscribed to Mixergy Premium about 2 months ago and it rocks.
I wrote a blog post the other day with a list of things you can do to afford Mixergy Premium in 2012[1] which is basically just me saying I think it's awesome and valuable and that $200 for 1 year is such a small amount of money that you can make it back in any number of really trivial ways.
Andrew also offers a 100% money back guarantee so that if you think the paid service is junk he just gives you your money back. Can't lose! I love it. Keep up the great work Andrew :)
Mixergy is awesome. The thing I love about it is that it gives you tons of things to try out.
No one single interview is going to give you the silver bullet for your business, though. In fact, many times you'll hear one interviewee say "Tactic X was wonderful" and then another say "Tactic X was worthless."
But there's so many good interviews and Andrew is great at extracting the core of the ideas that there's no reason you or I couldn't try the tactics and see how they work in our respective situations.