Aggressive PostgreSQL version upgrades
One habit some database deployments adopt that is counterproductive with PostgreSQL is the idea that the version of the software used should be frozen forever once the system is validated as working. This is a particularly a troublesome viewpoint for systems that are running into performance issues to adopt. The performance increases you'll find just from upgrading from older to newer PostgreSQL versions can be far larger than anything you can do just by tweaking the older version. Similarly, if you're running into a problem with how a specific query is executing, don't be surprised to find that it's fixed in a later version of PostgreSQL, and upgrading to it is really your only option to obtain that fix.
While major version upgrades like going from PostgreSQL 8.2 to 8.3 will introduce compatibility issues, you shouldn't expect that to be the case for minor version upgrades. If you're running 8.2.3 for example, merely...