I finally managed to get this working, sort of....
 
1) There's a 3-4 second delay from when you turn the rotary on the controller and when it actually changes the setting in the VST GUI (though the values change right away in the ACT grid). How do I fix this?
 
2) There's a slider that ACT automatically placed in the grid that shouldn't be there. How do I get rid of it?
 
All suggestions much appreciated!
 

Well, I solved the first problem, the delay. I deleted the track, saved the project, then recreated the track. Now it works fine. I probably could've just deleted the VST from the track and reinserted it, I'll find out if that works on the next VST I try ACT on.
 
Still have the unwanted slider mapping though....

So then I tried another instance of the VST on a new track. Didn't automatically pick up the mapping (like the support tech said it would). Opened up ACT, twiddled the knobs and saved. Now it works, with the delay problem. Went back to the original track, now it's got that problem too.
 
If I was getting paid for the time I've spent on ACT, I'd have a new Les Paul. This is WAY too flakey.
 
Here's a heads up for any other unfortunate who comes across this thread:
 
Buy Bidule ($99). It's a VST host that also works as a VST itself. Insert it on an audio track. Open it up and insert your MIDI controller (if your controller isn't listed, create a MIDI track and point it at the Bidule track) and the VST you wish to control. Connect the dots (literally). It's parameters will appear in the VST's right click selection "Control from MIDI". Straight ahead LEARN from there on. Save the Bidule. Next time you need that VST load Bidule on an audio track and load the SAVED bidule. Done and done. No flakes.
 
If someone who has real experience with ACT should happen onto this thread, and knows what's causing the problem I'm experiencing, I'm still interested in the solution.

For ACT mapping: http://www.azslow.com/index.php/topic,13.msg107.html#msg107
 
For visual delay. Some plug-ins show it, some do not. I think that is plug-in dependent (only) since the value is changed.
 
The schema is the following:
 ACT/MIDI learn/Automap/whatever -> VST Host -> (VST automation API) -> VST plug-in -> VST plug-in GUI.
 
And so:
1) if after turning knob the sound is changed, the mission is accomplished
2) only VST knows how to update its GUI. Sure, host can send "redraw", can mess with VST API, etc. But if VST does not want to draw the new value, host can not fix that.
 
That is an easy check either ACT is the source of delay problem:
Add Track Automation for parameter in question. Add some value to the lane. Move automation point. Do you see the same delay as with ACT? If yes, that is not ACT specific. If not.... there is some bug with ACT which should be reported.
 
Note, that the test as the rest is for ACT part ONLY. There still can be something wrong in Sonar -> VST Automation inter-operation. But that is outside of your original subject.  

My apologies to Cakewalk. After messing about with various hosts (including Bidule), it turns out that this particular VST (BIAS Amp) is the problem. ACT is still a PITA to use, but at least now I have a better handle on it. Sometimes we learn the most from trying things that don't work (paraphrase Thomas Edison?)!