I've used it, sparingly.  Glad it was there when I needed it.   I use it mostly for bass drums.  I have an OK mic locker, and can cover drums well.  Have a good sounding room too.  With overheads, room mics and individual mics on each head, top and bottom, I can correct for an odd placement here and there  EXCEPT when the bass drum is missing than beater sound. If it isn't there, its hard to bring back in with any of the other mics and if I can, it upsets the balance, unnaturally imho.
 
Now that I think about it - next time I track,  I will get a recording of single drum hits\mic combinations  just after setup, and see how I might be able to use them, and if I can - well that will be icing on the cake... 
 
LL    

I use it quite a lot, mainly in the following cases:
 
1/ I'm mixing drums that I didn't record, and I'm not happy with the sound of some elements of the kit.
 
2/ I'm mixing drums that I DID record, and I'm not happy with the sound of some elements of the kit. Oops.
 
In both of the above cases, the most common problem is just a badly-tuned, badly-maintained kit.
 
3/ I'm trying to add something to a pre-existing loop that has weak elements.
 
 
I think the most common thing in all cases for me is replacement or augmentation of the kick drum.
 

1. I wish the Dyn (Dynamics) control had an accompanying level control. 
 
Currently the control does slope and level in one and the result is not always what I want.
 
(Note: the Level control sets audio level, not midi level)
 
2. I also wish user inserted notes could be muted, like the detected notes.
 
3. Seeing the midi levels of the notes more easily would also be great. Currently it's necessary to inspect each individually.
The intensity of the marker is clever but not precise enough when comparing markers more than a screen distance apart.

dcmg
I had a client project that was a bit of a Pentatonix thing where most or all tracks were human produced.
Being able to take the human beatbox tracks, gate/EQ them then use Drum Replacer to augment the human sound with a touch of 909 type kick was crucial. Worked really well.

I've done this also.  To get better results I duplicated the beatbox track 3 times and eq'd to isolated the various elements...probably what dcmg did above.  The blending of the live and sampled drums was very cool.

Can't figure out my work with out it!