Do folks here buy into the REST == CRUD mapping the way it's basked into Rails?

I don't know... do you want to elaborate a little more on that?

For example, the pairing of PUT with 'update' , with only POST allowed to create new resource, versus allowing clients to PUT a new resource (effectively creating them) when given the proper URL.

See, for example, http://www.rgoarchitects.com/nblog/2009/06/23/CRUDIsBadForRE...

and in particular the idea that REST is about documents, not databases. "The data model is _not_ the resource model," as one comment there puts it.

Also, CRUD makes no allowance for HEAD and OPTIONS, as if they don't even exist.

I see too, in digging around for links, that this has been discussed on HN before (big surprise, no?): http://news.ycombinator.com/item?id=629843