Hey there,
I did MAPH in 2006-7 and just want to say that I had an amazing time. I met the most wonderful people. Yes, it's $$$, and yes, it's intense for many, but it was one of the most worthwhile decisions I've ever made. I do want to note that I was there when the "old guard" left and new directors came the following year. This will be their third year, I think, coming up, so they will have worked out kinks and have gotten more established, which is good. The main thing about MAPH was the sense of community that it fostered. If you go, take advantage of all the community-oriented stuff they have going on, like the weekly open bars on Fridays in the first quarter. You will meet really special, smart people, and have a MAPH alum community for the rest of your life, if you want it. The staff/admin are awesome, too.
Advice: Visit during campus days!!! The vibe you get that weekend will define the vibe of the following years in many ways, so get there and decide if it (and the campus) feels like YOU.
However, if you go, don't go with the sense that you didn't get into a PhD program and are there by default. Rather, be proud to be there. It's very rigorous and and you will learn a lot.
Good luck!