Q: Using cucumber for writing the functional requirements document for a Rails app In the light of BDD, would it be a good idea to use Cucumber features and scenarios to write up the functional requirements document at the start of a new Rails project?

A: Probably not. This would be a case of BDUF (http://en.wikipedia.org/wiki/Big_Design_Up_Front).
It's unlikely you'll be able to think of all the scenarios up front. You should split the high-level requirements into features to help estimate and prioritise them, but leave the detailed scenario writing to just before you're ready to begin implementing each feature.

A: If you are not the one making all the decisions and someone thinks you need these,
then it might appear to be a better choice than MS word.
I actually joined a project with a million un-implemented features,
so we had loads of integrations test in theory, just none
of them were actually implemented.
Its months later and we still have some,
its really difficult working in an environent where
everything is failing at once.
Its better to have 1 failing step at a time.
I also think feautures should be written by application developers who
understand user flow realities.
I like the business or client to explain stuff to me in a conversational syle,
a bit at a time, not their entire vision for world domination in 10 000 words,
I will keep that for bed time.
