After two years of service, RubyForge's PostgreSQL database backend now contains over 3 million records. Of course, 1 million of those are in the activity_log table, which gets a record inserted for every hit. activity_log is a rolling table; it gets truncated to the previous seven days of data every night. Otherwise it'd be massive.
The next largest table is frs_dlstats_file with 580K records, followed by stats_cvs_group with 350K.
The PostgreSQL data directory is at around 600 MB; storing all the releases in the filesystem helps keep that size small. And most people aren't uploading large documents to the DocMgr; if they were, the database would be getting pretty hefty.