I recently got a new laptop (Vostro V13 for anyone wondering) and need to re-setup all my stuff to work. Ruby and most tools weren't a problem but getting phonegap going on ubuntu was a bit of a challenge. One thing I remember that tripped me up last time I went down this path was a weird error I got when trying to run the command to launch my app:
$ cd framework && ant jar /home/vince/src/phonegap/android/framework/build.xml:49: taskdef class com.android.ant.SetupTask cannot be found
I remember spending a few hours on this last time, but this time around I remembered the solution is fairly easy. Just pop open your local.properties file in the frameworks directory and make sure the path to the SDK is correct. After that you should be good to go. Phew!
jar: [jar] Building jar: /home/vince/src/phonegap/android/framework/phonegap.jar BUILD SUCCESSFUL Total time: 3 seconds