Error compile in "Use Facebook Login example"
I had the same problem and it was because I forgot to add the com.facebook.LoginActivity activity to AndroidManifest.xml.
Also check that you followed the steps on the "Create a new Android Project with Facebook Login" section on https://developers.facebook.com/docs/getting-started/facebook-sdk-for-android/3.0/ , specially those regarding adding the app_id string to res/values/strings.xml, the INTERNET permission, the com.facebook.sdk.ApplicationId Meta Data, and finally the mentioned LoginActivity.
While the original question is related to SDK 3.0 I think it's worth mentioning that in SDK v4.0.+ the activity that needs to be declared in the AndroidManifest.xml is com.facebook.FacebookActivity eg:
<activity android:name="com.facebook.FacebookActivity" android:configChanges="keyboard|keyboardHidden|screenLayout|screenSize|orientation" android:theme="@android:style/Theme.Translucent.NoTitleBar" android:label="@string/app_name" />