Making Thunderbird faster

All of a sudden, after using Thunderbird for Mail, GCalendar, Outlook Calendar, RSS feed reader for half a year (or maybe more), it all of a sudden got slow.

I then learned about compacting folders:
http://kb.mozillazine.org/Compacting_folders#How_to_compact_folders
which has made it a lot faster (and doesn’t consume 90% CPU). However, it still freezes for a couple of seconds every 5-10 minutes …