From the YACCS site --
2. Why are you making this change?

For technical reasons. To keep YACCS running as smoothly as possible, the entire database is cached in RAM. However, the database is now larger than available memory. I can't afford to buy more RAM (or a few SCSI hard drives in RAID configuration), so I had to pick a subset of comments to be accessible.

Well. I think we've answered the question as to why YACCS runs so slowly. Sounds like the biggest blog comments service runs on this guy's desktop. Amazing.