As objects are deleted, Frontier monitors their freed-up blocks so they can be reused, as Matt Neuberg describes in Frontier: The Definitive Guide:
... as the database is used, free space opens up in it, and pointers to the free blocks are added to a list called the "avail list," which must be traversed each time Frontier searches the database. This strategy makes saving and accessing the database rapid and robust in the short term, but over time its accumulated effects reduce the database's efficiency.
I took Buzzword.Com offline this evening for 90 minutes to compact all object database files and wipe out these avail lists. I'm hoping that it improves the server speed; users should let me know if it's making a difference.
Update from Craig Jensen: "Longtime blogging friend Garret Vreeland says he can connect to BookNotes in less than 5 minutes. That's progress!"