i've read that you can't 'pre-book' seats for theaters that have reserved seating a la fandango. you have to wait until you get to the theater to choose your seats. if they can fix this, i'll subscribe right away.
You have heard correctly. MoviePass requires you to be physically present at the theater before "checking in" to the movie for which you intend to purchase a ticket. Only then can you use the MoviePass Mastercard to buy your ticket.
So you can pre-book and reserve seats, but only in person. If you live very close to a theater, you could pre-book at lunchtime and come back that evening to watch the movie, for example.
It definitely requires you to be physically present, though. There is no online ticket-buying with MoviePass.
Some theaters let you reserve seats. In my region, none do. Luckily, in my region, most theaters do "$5 Tuesday", so everybody goes on Tuesday or Friday/Saturday night. Any other day of the week, at any time, is basically empty, so it's never been a problem.
I just checked, you can do either. For my local Century 16, they allow ticket purchase and reservation of seats to be done on either cinemark.com or fandango.com.
So you can pre-book and reserve seats, but only in person. If you live very close to a theater, you could pre-book at lunchtime and come back that evening to watch the movie, for example.
It definitely requires you to be physically present, though. There is no online ticket-buying with MoviePass.