Hi
Yes you are right ,but not just pan and volume but EVERY parameter that plugin has. (if it supports DX automation).
Lets say you have a song that you want to change the reverb length time or room size.
You would select the parameter Room Size a edit the envelope where ever you want to make changes.

Right now off the top of my head I think,
Waves 3.5
PSP
Sonic Timeworks (newer stuff)
Arboretum (later this year)
RBC Voice Tweaker Pro
SpazTek Filter King
Izotope (later this year)
have the DX automation.

Im hoping that the new Acid 4 and Vegas 4 will support DX automation. All we can do is hit Sonic Foundry up for these features.

I've been playing around with it in Sonar its pretty cool.

George Ware