Is the data associated with an app cleared when an app is uninstalled?
As Matthew Read noted in a comment: yes, it is. The entire data directory is simply deleted:

C:\Console2&gt;adb shell ls /data/data/com.chessclock.android/
lib           shared_prefs

C:\Console2&gt;adb uninstall com.chessclock.android
Success

C:\Console2&gt;adb shell ls /data/data/com.chessclock.android/
ls: /data/data/com.chessclock.android/: No such file or directory

#Reinstalled from the Market at this point

C:\Console2&gt;adb shell ls /data/data/com.chessclock.android/
lib


The shared_prefs directory is absent in the last ls listing because I didn't launch the app, I only reinstalled it, therefore there were no preferences yet created for it (it sets defaults on the first launch). I point this out only because it illustrates that the preferences from the previous install were not retained anywhere.