Error running [...]: No valid Maven installation found. Either set the home directory in the configuration dialog or set the M2_HOME environment variable on your system.

To fix, you have to add M2_HOME variable in the Mac specific way.

Create or modify the file ~/.MacOSX/environment.plist, and add an entry for M2_HOME

If that file is already there, you may find that you can’t edit in a text editor because it is a binary file. First you will have to convert it to plain text (xml), edit it, and then you can convert it back to the binary format.

$ plutil -convert xml1 environment.plist

$ vim environment.plist

$ plutil -convert binary1 environment.plist

Ref: http://youtrack.jetbrains.net/issue/IDEA-21225 and http://devnet.jetbrains.net/thread/278634

I use Intellij IDEA, and the main problem for me was that, after building the application using the Ant build script created by activitycreator tool, you have to manually reload the application in the emulator.

This is easily fixed by tweaking the generated Ant build file.
Add the following target to the build.xml -

 <!-- Main activity -->
<property name="main-activity" value="MyMainActivity" />

 <!-- Run the main Activity after reinstall -->
 <target name="run" depends="reinstall">
 <echo>Running ${application-package}.${main-activity} on default emulator...</echo>
 <exec executable="${adb}" failonerror="true">
 <arg value="shell" />
 <arg value="am" />
 <arg value="start" />
 <arg value="-a" />
 <arg value="android.intent.action.MAIN" />
 <arg value="-n" />
 <arg value="${application-package}/${application-package}.${main-activity}" />
 </exec>
 </target>

MyMainActivity is, of course, your main activity. Remember to change the build file if you rename or change the main activity.

I also changed the default target to run, and after loading build.xml as an Ant build file in IDEA, I assigned it a shortcut key.
I also made these changes to ANDROID_SDK/tools/lib/build.template, so from now on, when I create a new Android project, it is already set up this way. If you are editing the template file, use -

 <!-- Main activity -->
<property name="main-activity" value="ACTIVITY_NAME" />

This will automatically pick up the class name you specify on the command line when running activitycreator.