The lack of trial versions aside (which is still a huge problem), one of the primary issues with the MAS is the flat-out exclusion of certain categories of application. For example, system utilities are almost totally banned from the MAS, and the system tools/ utilities that are currently available in the Mac App Store tend to just be slimmed down versions of their non-MAS counterparts with lots of functionality removed.
I speak to hundreds of OS X developers every week, and the sentiment around the MAS is gradually changing. Typically we're hearing developers just referring to the MAS as a marketing channel these days, due to the restrictions enforced on them.
We see a lot of data around MAS vs. Non-MAS sales, and reasons for developers switching, so if anyone has any questions about this space, I'd be happy to answer.