In our case we used Titanium. Would I chose to use it again? NO!
To further John's comment, these cross platform IDEs have one requirement no one tells you about: Who ever uses it to develop MUST know very well the platform on which is developing. These IDEs MUST not be used to compensate lack of knowledge into an specific platform. Hence, the programer must know very well iOS and/or Android. Why? Because these IDEs impose an extra layer over the entire project. If the developer doesn't know an specific feature of the mobile platform and relies on the IDE to cover it, you'll have a mess of a project, costing in the end far more than having coded it natively in the beginning.
So it doesn't only requires knowledge of the IDE, it also requieres knowledge of the platform to which you are deploying. As you can see you now have two requirements, than a native programmer doesn't have.
Of course, if you're doing a simple app, then its not big deal, but even doing a simple app, the UI will suffer if the programmer doesn't know well either iOS or Android.
Going specifically with Titanium, this platform works with plug-ins, which in theory are great. You just put you plug-ins into the project, few lines of codes are needed and boom! you're done!. The thing is that not all plug-ins are kept up to date. As such, expect the feature of a native SDK being ahead of the plug-ins for Titanium. We experienced this with the Titanium AdMob plugins. It was several versions behind with what the AdMob SDK offered. These plug-ins are not responsibility of Titanium, are a responsibility from the third parties. You can see then how the mess starts to add up. The same with Analytics, Flurry, or any other SDK you want/need to integrate to your app.
Phonegap is very popular because allows programmers with zero knowledge of Objective-C or Java, to make apps for mobile platforms. If the programmers are under this scenario, you can't beat that! But notice that if the programmers don't know the platform, the ride will not be smooth. I'm talking more challenging than the normal challenges any software project has.
In our case, the next version is going to be native, using Titanium or another cross platform IDE requires in the end more effort than doing it natively, at least that's our case. I'm sure others will have different experience.