Anyway, the bottom line is that after a lot of mucking around in the code, I've limited the performance damage to the point at which you choose a favorite on the left-hand menu. Sometimes you can switch between favorites as fast as normal; sometimes, though, it can pause for a significant amount of time, which I believe is QSettings trying to sync with the flash storage. I'll keep working on it, but I'm not sure whether I can improve it significantly; in the end it may be quicker to just remove this feature and go back to navigating to the panel collection you want...