I am learning this via Sams Teach Yourself Android in 24 hours.
This is really strange, I run the app in the emulator and I get my splash screen (just some crappy text really) then I press the home button, and click on my app's icon and it gives me "Application is not installed on your phone"
I went into the emulators settings->applications and it's there!
I cleaned the project, uninstalled it from the emulator and re-ran it. Same damn problem.
(project is simple: 6activities, each has a unique text, as it starts it shows the splash activity I have not even connected the other activities... just this)
You can download the entire source if you want at http://elxotica.com/TriviaQuiz.rar