Following up on the positive experience I had recently with another of Packt Publishing's "Instant" titles for Postgres, I picked up a copy of Instant PostgreSQL Starter and dove right in. (And I must say I'm enjoying these short format books.)
As a brief aside — I think the author's choice of going down a fairly platform agnostic path by utilizing +EnterpriseDB's installer and interacting with the database through pgAdmin3, rather than psql in a shell, was a good one. It provides a one size fits all approach for anyone to get up and running without having to delve into the nuances of shells on different systems, various installation methods, and so on.
What I think was the most valuable portion of the book for me was "Top 9 features you need to know about", which gives an overview of such topics as hashing passwords for storage, XML in Postgres, and full-text search, to name a few. For someone coming to Postgres from another database, it's learning about these kinds of features that truly help you get up to speed a bit faster. And I appreciate being able to get a brief overview of these topics in order to simply know about them and how they work, without becoming an expert in any (just yet!).