10.6.9 is perfectly safe, UNLESS you use FxFactory plugins that do tracking (and facial recognition?). The tracker FxFactory uses got broken. Seems code from iPad version, which doesn’t support plugins, ported to FCPX desktop version, broke some FxPlug4 stuff… AGAIN! That’s two seriously broken versions within three updates.
Yeah, found this out this morning. I don’t typically use tracking in a text wrapper (for me it’s CoreMelt or Motion/built-in) so I’m going to roll with it, but definitely sent FCP feedback to Apple about it – there’s an article on FX Factory’s site about the issue: