Two quick pieces of advice:
1/ PQA Query time analysis : http://pqa.projects.postgresql.org/
This tool will tell you, over time, which queries are run most often, which are the longes to run etc.
2/ The postgres performance email list : http://archives.postgresql.org/pgsql-performance/
It's moderate traffic, the archives are good, and people will spend time with you problem as long as you post enough info in your question to give them something to go on.
