Useful Postgres Statistical Queries

[rockstarTS]

I'm putting together a monitoring solution for postgres and have read up on how to get Postgres to gather stats. My problem is that I'm not a Postgres DBA so I'm not sure what are the best queries to run to identify problems. More specifically, I'm looking for useful queries that sample the gathered statistical data to either identify a problem or get a numberic value to apply a threshold.

Are there any experienced postgres DBA's out there that are familar with the stats collector that can recommend some queries that are useful in monitoring postgres and explain why they're useful?

Thanks.