The short introduction to CouchDB at
http://blog.couchone.com/post/1167966323/a-gentle-introduction-to-couchdb-for-relational
is a fantastic writing example. Within a few paragraphs the author has conveyed the essence of the tool and for an experience tools user/evaluator the set of next questions that must be answered before it can be put to use -- security, contention, document size boundaries, etc -- can now all be asked discerningly.
