I listened to the guys from Alaskan Brewing Company speak about their mash filtration equipment at the last year's CBC. I was trying to find the presentations in the midst of the "Attendee Bag" schwag, but I'm not finding it. From what I recall, their justification was two-fold:
1) Efficiency (as stated)
2) The cost of shipping wet, spent grain became a huge factor. Being in Juneau, they had no local source to offload spent grain and had to ship it to the lower 48. With the mash filter, they were able to extract more wort from the "grain bed" thus reducing the residual moisture content of the spent grain and the resulting shipping costs.
The biggest cons they talked about were the change in milling and the lost ability to do small batches. As Tom mentioned, they had to invest in a new hammer mill, and there was a relatively narrow production band for mash sizes -- i.e. they couldn't produce huge beers, small beers or lower volume batches.
IMHO, I think wide adoption is going to be limited to the larger regional breweries with established brands who are looking expanding with new plant builds. Even then, I have a hard time seeing established breweries adopt the technology at the same time as a major expansion. Maintaining consistency throughout those kinds of changes seems like a huge undertaking.
I'm interested to see which way New Belgium and Sierra Nevada end up going with their Eastern US expansion plans -- speaking of, has anyone heard if mash filtration is in either's budgets?
I'll dig around a bit more and see if I can come up with the slides from the presentation or at least more info.