Postgres query plan of a function invocation written in plpgsql
I addition to @rfusca's advice: SQL statements inside plpgsql functions are considered nested statements and you need to set the additional Parameter auto_explain.log_nested_statements.
Unlike some other extensions, you don't have to run CREATE EXTENSION for this one. Just load it dynamically into your session with LOAD. You must be  superuser for this.
Your session could look like this:
LOAD 'auto_explain';
SET auto_explain.log_min_duration = 1; -- exclude very fast trivial queries
SET auto_explain.log_nested_statements = ON; -- statements inside functions
-- SET auto_explain.log_analyze = ON; -- get actual times, too
SELECT * FROM get_paginated_search_results(...);

May produce a lot of log output.
The current manual on auto_explain.
Depesz wrote a blog article about it when it was introduced with PostgreSQL 8.4.