Newbie! I've got Titanium 1.2.1 with the Mobile SDK 1.4. I created my project fine and when I run it the emulator starts but the hello world app is nowhere to be found. I've tried it with the Android SDK set to 1.6, 2.0 and 2.2 same behavior. Nothing in the WARN or ERROR log.
This fixed itself after restarting Titanium.