Appcelerator claims Titanium is "70% faster than developing in Objective-C" (appcelerator.com)

and 45% of statistics ending in 0 or 5 are made up.

I call BS. I actually just finished a project that we first evaluated Appcelerator and Sencha as a cross platform solution.

I can say the only time I would ever recommend either is if you have complete control over the UI and design of the app - meaning go with standard look and feel of either framework, but don't expect to easily go beyond that.

If however you have a client come to you asking about cross platform, and they have a designer or their own vision for how the app will look - stay away from these "cross platform" frameworks. You will quickly be backed into a corner.