First off I'll say I am a very happy Mercalli user.
However, in wishing to explore further Mercalli usage/flexibility:
1] Place Event on T/L
2] Add CC + Magic Bullet Looks + Merc (I'm guessing that any ole fxs will do?)
3] Have all FXs unchecked except Merc
4] Click CC Fx to raise the FX timeline
5] Merc is showing its OWN Fx timeline (please note this!)
6] Attempt to add a Keyframe to the "Merc" Fx timeline
What result do you get? I get a Vegas "hang".
Now, I can imagine that this would happen as Mercalli does its thing to the WHOLE Event, and logic tells me that this should be the case. But a VegasPro8 "hang"? As it happens, the Merc Menu doesn't include an Fx  timeline. Maybe this should be ironed-out?
Please check
Grazie