Titanium has been deployed in over 12,000 apps in the Android Market/App Store, more than any other cross-platform framework (that we know of), so many developers have found success using it. That said, no technology is a silver bullet, so you'll need to take a look at your application and decide what is the right move for you.
If at some point while using Titanium, you discover you need more native functionality than we currently expose, it's easy to write a native extension (well, easy if you know Objective C and Java). Guides are located at:
Despite the success we see every day by devs using the platform, Titanium can be a bit flaky at times - and I'm sorry to hear some folks have run into problems with their specific use cases. Feel free to reach out to me directly (firstname.lastname@example.org goes to my inbox) and I'd be happy to help out.
EDIT: We actually just demoed an AR app using the device camera, but the source isn't up yet (not sure why not, but it will be open source). If you follow our dev blog (developer.appcelerator.com) or keep up with our GitHub account (github.com/appcelerator), the source will pop up there.