I have tried repeatedly to use AudioSnap and have done nothing but waste a lot of time.  I have followed the online help and a few of the internet tutorials but have yet to get it to actually work.
 
I have to ask if anybody uses it and is there some magic key that I may be missing?

I use it often, primarily for lining up double-tracked vocals and harmonies. But I use it almost exclusively for manual timing edits, dragging transient markers by hand. 
 
I have also used it on a few occasions for creating a tempo map from live recordings that weren't recorded to a click. It worked quite well for that, allowing me to perform drum substitution and to layer sampled percussion over live drums.
 
Is there a secret to using it? I don't know. I only use it in these two scenarios, and I haven't strayed from the basic methods that have worked. I can only tell you that yes, it does work (quite well) in the limited ways that I've used it.

Me too, Not very often, but it is Brilliant at generating a Midi Kick or snare from audio. 
It works best with tracks that have very strong transients. I don't think it works at all on mush. 

I use it as a manual editor and it works pretty ok.

Most of the tutorials emphasize beat slicing and stuff, but I think its strength is with time stretch that sounds pretty ok.

That was my initial try was using it to beat match an audio file.  It does map the transients but the tempo it then suggests is usually WAY off (ie 124 actual but audiosnap says 170).  When I try to move the measure markers around, like using control+drag to move say 11:1 to where it shows 14:3, when I drop it it goes back to where it was.
 
On the opposite side, I tried to take a clip and change the tempo and I never got it to work either.
 
I have to guess I am missing something.

AudioSnap needs nice clean transients to detect tempo properly.
 
A kick drum track works best. But if all you have is a full mix to go by, you can create a click track yourself by recording a percussive sound as you play along with the song. Or record a MIDI track and render it to audio with a synth, which will be easier to correct any playing mistakes. Then let AudioSnap decipher the click track. It's an extra step, but it works every time.

the older versions of audiosnap didn't work as well as the newer versions in X2 & X3. (even X1 had some flaws that caused me grief).
 
I don't use the automated deal for AS, I use the transient markers to move them manually where I want them and that works out great for me.

bitflipper
AudioSnap needs nice clean transients to detect tempo properly.
 
A kick drum track works best. But if all you have is a full mix to go by, you can create a click track yourself by recording a percussive sound as you play along with the song. Or record a MIDI track and render it to audio with a synth, which will be easier to correct any playing mistakes. Then let AudioSnap decipher the click track. It's an extra step, but it works every time.

Thanks for the suggestion. I'll give that a try.
 
I can usually get close to the tempo with trial and error. I was just hoping it would be easier...

I've fallen back to trial and error a time or two myself. It only works if the original track was recorded to a click and is therefore consistent from start to end. Real music played by humans rarely comes out that way, though. In fact, the best music never has a single BPM value from start to end.
 
Check out this blog post: http://musicmachinery.com/2009/03/02/in-search-of-the-click-track/
 

Interesting how much using a click track can make so much of a difference. But yes, I have a tendency to speed up during certain sections or slow down during a bridge or whatever so it is understandable. I wonder how Buddy Rich would stand up the graph. :)
 
The only reason I'm doing this is to import songs to use for Christmas lights - bringing the song into Cakewalk and then adding midi for show control.  Using the tempo/time change markers do help some but those just add more trial and error as well.
 
I would like to submit an ELO song to the guy in the article. Talk about the tempo being all over the place. Not only do they use lots of ****s and tempo changes but I would imagine each player is a little off as well.
 
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Edit:
I guess I should use ****ando for r-e-t-a-r-d?
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Edit edit
r-e-t-a-r-d-a-n-d-o! egad!