I've had my two girls for about a year and a half now. In the beginning, bonding went perfectly (thanks to loads of helpful advice on these forums!). I quit smoking a few months back and my lovable, bonded girls suddenly turned into little she-devils with crabbing, lunging, and biting (much bloodshed). It took me a while to figure out why they were suddenly not my little cuddle buddies anymore.
Now that I know "mommy tree smells different (and better!)" i've been working on re-bonding. We started out with the very basics. It's been a few months now and today, out of the blue, one of my girls got spooked, ran down my shirt, and hid in my bra!! I was THRILLED even though it was slightly awkward given the fact that there were people watching as it happened. Several hours later, her sister was climbing around on my shoulder and so I lifted my shirt and sure enough, she joined her sister for a long nap between the girls .
Bonding a second time has taken much longer than when they were joeys, but I would say that as of today, we are successful in our attempts! All it takes is a lot of love, patience, understanding, and of course treats haha.