I was pleasantly surprised by Titanium mobile though when I had to evaluate it at my job 2 years ago. I set to reimplement one of our (non-trivial) apps and summarize my experience. I ended up writing 50% less code and it took about the same time as what I had spent on the native version. I consider this a compliment though as I was completely new to Titanium. On the flip side I was completely new to the app when I wrote it the first time :-)
The build/run/debug loop was unpleasant but I've heard that it has improved since then. As for performance, it was good - Titanium generates native UI, albeit with an interpreter in the middle.
I was quite surprised when it turned out that I have a 99% identical app. You see, from the very beginning I decided that I'll be hard on Titanium, my goal was no-compromise, high-fidelity clone. And it worked. The only problem was positioning a tooltip near a touch point - at the time there was no way to traverse the view hierarchy. But then again, maybe I could have implemented it in a different way.
I realize a lot has changed since than, but this is my 2 cents - sharing a real world/product experience.