Prototyping is good tool; if your regular development is slow, not agile and
you need to draft something up real quick for your client.
If you're a Rails developer / designer, why even bother? Why not just start
pumping the business up? You don't have that much attrition to get an app up
and running. All the time you spend in prototyping should be invested in
building the actual app.
Web application design walks with its development, they are too close to be set