I'm with the OP on this one, too. I use an MUP very consistently through much of the year for commuting (the Charles River MUP- Boston side of Charles). I avoid it at times when it's way too busy and take to the streets but most of the time I love it.

I also use MUP's on tours- my annual trek to Provincetown I ride the Cape Cod Rail Trail, in The Berkshires I ride the Ashuwilltocook as part of my 80 mile loop to Greylock.

I don't kid myself nor do I mean to try to convince anyone else that they are a panacea and solution to all cycling ills but they certainly have their place and I am ever thankful they exist at times.