Some thoughts on using node-postgres in a web application
This is the approach I've been using for the past year or so. I'm sure I'll change and it will change as I grow & am exposed to more ideas, but it's worked alright for me so far.
I would definitely use a single pool of clients throughout the application. node-postgres ships with a pool implementation that has always met my needs, but it's also fine to just use the require('pg').Client prototype and implement your own pool if you know what you're doing & have some custom requirements on the pool.