I have a new tune.
I melodyne tempo extracted an initial guide track - there are tempo issues.
I stupidly recorded a bunch of instruments, had some magic happen but the tempo issues need addressing.
 
In the second chorus the tempo slows.
I draw a line for the tempo in that section and as expected all hell broke loose against the midi drums.
I undid my tempo edit so everything would return to it's crappy normal.
Never having done groove clips before I muted everything but the drums and the guide guitar track then
created a grove clip from the guide track that is the length of the shaky chorus. Then I flat lined the tempo
again in the chorus section and this time it worked perfect the midi drums and the analog guitar track truck along
perfectly.
 
This makes me want to groove clip all the tracks.
 
Is this wrought with trouble ahead?
 
Audiosnap and I are at odds with one another btw.
 

Wish I knew, but I don't... I will give your method a shot though--it looks promising!

After listening again it's kinda artifactly.

Bounce down the clip before you decide, the online algorithm is much worse than the offline one.

I gave up and retracked it today using a basic beat from a drum machine to keep me hovering around the bpm as I made the guide track. I tried not to lock tight to the drum machine and hoped that the resulting tempo map would have some variation which it did. This resulted in a controlled yet groovier track than quarantizing to a more ridged clock.
 
So much for my personal delusions of tempo grandeur.

I have made 100's of songs and most of them start with me on acoustic guitar playing to a drum pattern. I dumped all the patterns from my trusty old Roland 505 to midi 20 years ago and I still use those almost daily. 
It's a myth that a song won't sound "human" if it's locked to a continuous tempo. baloney,  All that "humanizing" and what not just make things worse.  Do not fear a steady groove. Its all good stuff. I've played in bands that are tempo solid. We would be recording 4 minute songs and each take would end in almost the exact same spot. 
You humanize it by adding real instruments which will all be just a little off the beat but hopefully in a musical way. Drums.Bass and keyboards should be locked in tight,, lead guitars and vocals are allowed to be loose gooses.  

Me too, but I was frustrated with the lack of swing. Especially from beat 4 to beat 1 of the next measure. The tempo extraction of melodyne and sonar is a very welcome addition for me. Provided that I can provide good source material.

For a 100% accurate tempo map, I personally go the manual mapping way of turning on the click, opening the tempo view and hand drawing the tempos while the music plays. If the click starts to rush or drag, simply draw in the appropriate tempo change in the spot where it rushes or drags. When I'm done it's clicking perfectly in sync and I know the map is precisely the way it should be. After that for me it's slip editing the beginning to zero and bouncing the clip into place. Then I highlight the clip and open the audio snap pallete view, click Clip follows project (auto strech). Now at this point the tempos can be redrawn to desired tempos (or delete all tempos but one in the tempo list, you can change it there too). NOTE this is Online rendering in Groove-clip mode and once the desired tempo/tempos are acheived will sound MUCH better when bounced down using radius Mix. Don't give up hope! Any way I can help let me know! You can dropbox me! I did finally get around to trying melodynes tempo extraction and for a conducted orchestra peice with a full band and it couldn't stay on beat to save it's life. I've been hand mapping for years and find it relaxing and reliable! March to the beat of your own tempo map!

You're more patient than I am.
I'm so used to giving / receiving a quick scowl among band mates that I am spoiled now.
 

There is a better way so long as you kept your tempo within tolerance and didn't drift too wildly. I haven't actually tried this yet, but I heard that you can drag and drop your audio clip on to the time ruler and that will make Sonar's tempo follow yours. I.e any tempo changes/drifting you did, will be sorted by Sonar automatically. Then add Addictive Drums or such like and it will stay in time with you! As I say, if you drift off too much it will be noticeable as everything will slow down/speed up together, but then you can also use that for say, an outro slowdown or any other intended tempo change.
 
And talking of click tracks, guide drum patterns and drummers keeping tempo, I have almost always given drummers a click track to follow, even back in the days of tape when I started out. This is because they are coming into the studio to produce a refined, polished version of a song, often to go on an album. Unless you are going for a live take, always use a click. Not only does it ensure a consistent tempo throughout the song, but it also lines up the DAW with the song making it easy to work with, edit, sync to and for the other musicians to stay in time with. The best drummers are those who follow the click precisely but drift in and out ever so slightly while still staying bang on if you know what I mean.