Titanium was quite good
... used to use it for mobile dev.
I gave up with it about 3 years ago because while it lets you do some stuff cross platform, there was just too much more that needed to be done for each platform you published to.
The end result was that it took just as much time as two native apps to make one with Titanium, but clients saw the words cross-platform and thought "half the cost".
I know people who did great cross-platform apps with it, but I wasn't going to bet the farm on single platform that just not improving very quickly, bugs in APIs didn't get fixed for ages... they were too focused on making an IDE to improve the core product.