Okay. I don't use DR much, or any soft synth for that matter. But, when I do play with DR, I find that audio samples hit fairly accurate. At least, enough to work with. When I drag MIDI however, it starts hitting fine ... but quickly begins to be off-time pretty bad. I'd love to try some drum replacement with Addictive Drums, but the timing is so bad, it's unusable. I could probably audiosnap to the original performance, but I feel like it's not supposed to work like that.

What am I doing wrong? I'm following the documentation (e.g. setting a midi extraction note/value and dragging it onto the AD track).

I recently used exactly this method to change the drums over on 200 projects and drag/drop onto a midi track worked perfectly. 2 questions just to carify:
1. Are you saying that when you open the newly created midi track the notes appear out of time in the PRV?
2. Are all of the drums on a single track or do you have separate kick/snare etc?
 

1. If I remember correctky, it places the midi notes out of time. I considered quantization, but then I lose the natural swing in the performance. (I'm not near my system right now).
2. Multi-tracked drums. Each on its own.

You know ... I just tried it in a new project, with nothing else going on.  It seemed to work fine. Maybe, just maybe, when I get the itch to do some drum replacement, its typically further along in the mix, when I just can't dial in a tone I like.  This would be after I've got 24-plus tracks with different plugs.  I'm wondering if all that variation is causing some sort of delay compensation when I drag this to MIDI (I really have no idea what's under the hood with Sonar). 
 
Anyway it seems to be tighter than a frog's ... well, you know ... when it's by itself.  If I need to do it in the future, I'll just open up the track in its own project, process it, then pull it into my main project.  No big deal.

Interesting. I didn't run into that myself (24tracks +) but probably using different plugins. If that is what is causing problems you could just enable the bypass all FX button, then enable drum replacer and create the midi track, then cancel the bypass all fx button.
 
If you are still interested in tracking down the issue, clone a single track of the original drums (say the kick track), remove the drum replacer region fx from it and solo it, then also solo the new midi kick track you created and see if they are in sync.

So, I just accidentally stumbled on a video that showed how you can simply drag audio onto an instrument and it populates as midi notes. Hmmmm .... how long have I had this power at my fingertips?

The feature was introduced with X3.