I used to be a Flash developer who could code AS3 apps for web and export to mobile devices. I was never really on the “lets all hate Flash now” bandwagon, but I knew it was inefficient in a number of ways. It never really felt clean or fluid that I couldn’t tell it was made in Flash. With Titanium (the Appcelerator framework), I can still “feel” it a little bit (take that as you want), but to the average end-user it looks and feels like a native app.
One thing I’ll say is I’m not a huge fan of the Titanium Studio IDE they provide. I realize it’s based of Aptana Studio, but there are a few bugs within it still (code colouring doesn’t work half-way down a file, autocomplete not working sometimes, etc.) but for the most part it works great. You can compile/build your app right within the IDE and it usually goes off without a hitch. On iOS it opens up iTunes and you can sync to your device (provided you have an Apple Developer account with your device provisioned). Something that I found was if you open Xcode with your device plugged in and go the organizer and then your device console, you can see your console.log() events appear as you do stuff in your app on your device. It’s REALLY handy to debug a few device specific problems (camera, geolocation, etc)