postgresql.conf ships with quite modest defaults so be sure to august it for anything more than light use. We recommend for ~4k users;

• Available Memory = System Memory - OS (1GB for Windows) - Java (100 to 512)
• effective_cache_size = Available Memory / 2
• shared_buffers  = effective_cache_size / 4
• max_locks_per_transaction = 512
• max_connections =  60
• checkpoint_segments 30
• log_min_duration_statement = 10000
• log_line_prefix =  ''%m: ''

There is a convenient config creator here.