mwForum
I'm running a forum on shoujoai.com (software is mwForum; hardly anyone knows about this forum software but I think it has better usability than phpBB and vBulletin... at least when it's not on an overloaded server) that has 579k posts. It is on a P4 2GHz (512 KB) with 1 GB RAM and 80 GB IDE.There's other sites on the server but this site is probably by far the largest. It's getting overloaded; I think the lack of SCSI is the bottleneck, as vmstat shows ~500 bi and ~1500 bo.