I'm not seeing the lag you are. Even on a dial-up, it's pretty responsive.

As for the database, my esteemed colleage Krow and I have discussed some enhancements in the past. He's responsible for most of the brilliant speed improvements in Slash. I suspect his best idea is to gather all long text columns into a separate table, leaving document-nodetype derived metadata in smaller tables. Unfortunately, that's not on either radar at the moment.