I will do a 10-second FW dip (and vigorous shake) on any corals that are coming from a tank that has flatworms. Other than that, I don't bother.
(Excepting an elegance that we managed to keep for a year and a half. We did a rather elaborate
malachite green dip on that one, as we'd heard that it helped in keeping the now-touchy species.)
I also don't bother to quarantine inverts - just a slow drip time. Corals get dripped for about 1 hour (depending on how much I have acclimating) and maybe 2 hours for snails. Starfish, esp Linkia sp. get up to 4 hours of drip time. (Mostly because I'm paranoid with that species.) So far, so good.
JMO,
Danielle