I've cleaned up the database model, many of the SQL queries and statements, as well as the XSL templates. This has resulted in greater performance across the board! The most noticeable improvements are in the general ledger and the journal views.
I also removed some other pieces, like the account parent column of the accounts model. PBooks is going to use account groups instead, and these will be fully user customizable. The account types shall remain mostly static and reside in an XML file.