I've had suspicions about Spybot and Teatimer (which I don't really understand) but have taken the view that in the end the system "does something" in terms of increased security. If this is so then by now I can live with the long boot times. If SB is truly redundant then I can disable / delete.
Looking at Process Explorer during boot up (not easy to understand!) I get the impression that Avast takes up quite a bit of available system resources, which is of course reasonable if it is protecting me.
My version is Avast Free 6.0.1203 (on Windows XP). I have not yet psyched myself up to uninstall and upgrade to v 7 ...