Ken,
I'm afraid I don't have extensive experience with Fusebox or
Mach-II so I'll mostly speak towards Model-Glue. Unfortunately the
encounters I had w/ Fusebox were early implementations that perhaps
weren't the most efficient example.
Model-Glue is hands down geared towards OO development which
CF code does not have to be. From what I know Fusebox was pretty
procedurally oriented, it's only begun using CFCs in version 5.
What I like about M-G is the forced separation of presentation and
model. It's got a bit of overhead, but I've never noticed
performance issues running it. Another thing I like about the
framework that it's actively looking to integrate with other highly
useful elements such as ColdSpring and Reactor.
I don't believe Model-Glue has much of a learning curve and
with OO designs becoming more prevalent in CF, I think it's a good
framework to learn and will be in use for some time. For reading
material I would recommend the QuickStart at
http://docs.model-glue.com.
There was an article on CFDJ
http://coldfusion.sys-con.com/read/176171.htm
that might be useful. Also you can just Google the topic, there's a
lot of blog entries out there on it.
My recommendation though is to hit the QuickStart and then
try to convert a small existing app that you've personally written.
Working through that conversion you'll see the opportunties for
efficiently designing your app.
-Tim