i think the most sparsely attended show i've been to @ 930 was probably hank III in 2001 (june sometime?).
overall, though..
i saw mono in charlottesville back in 07 shortly after UVA had let out for the summer and there were maybe 30 people there. in the middle of mono's set i was able to walk up to the edge of the stage.
back in 2002 i saw explosions in the sky (with opening act coheed & cambria) @ hole in the wall in richmond. there were about 25 total people at the show. it was a very small room and it wasn't even close to crowded.
other than those three shows, i can't really think of anything i've been to that's been particularly empty. claypool @ the norva in 2001 right after it opened was not very crowded, but it was at least half full.. which is still ~500 or something?