[Lizard]

Rebuild your database periodically. It's an option in the File menu. How often is periodically? That depends on how many changes you make in a given time period. I might guess at once per week to start, and if you notice mid-week that it's slowing down again, do it more often.

If you need more performance than that gives, collapse any groups (Projects, Folders, etc.) that you're not actively using.