Compatible with Cordova 2.1.0 (older versions not tested)
Should work on Android versions down to 2.1 (SDK version 7)
You can register a callback function that is triggered when the selected tab changes
Only tabs implemented (with text or icon), no other features of ActionBarSherlock
If a tab is reselected, you won't be notified (TODO)
Tab creation only from Java code, not from JavaScript (TODO)
Cannot show/hide tab bar at runtime (TODO)

Setup

Download ActionBarSherlock and add the library folder as Android library project (see ActionBarSherlock documentation)
Reference the library project in your own Android project and make sure both compile
- They must have the same Android support library JAR file, if any (same file checksum)
- You may have to change the compiler settings to use Java 1.6 (right-click project, Properties > Java Compiler)
Copy ActionBarSherlockTabBar.js from assets/www to the appropriate location in your project (e.g. assets/www)
Copy the src folder to your project
Refresh your Android project (click on project name and press F5)

Now change your main activity (the one deriving from DroidGap) like this:

public class MainActivity extends DroidGap implements ActionBarSherlockTabBarPlugin.OnInitListener
{
    private ActionBarSherlock sherlock = ActionBarSherlock.wrap(this);

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        ActionBarSherlockTabBarPlugin.setOnInitListener(this);

        // The following two lines have nothing to do with the plugin, just good practice in my opinion:

        super.setIntegerProperty("loadUrlTimeoutValue", 60000);

        // Show splashscreen up to 25 seconds (hidden when application is ready, see JavaScript code)
        super.loadUrl("file:///android_asset/www/index.html", 25000);
    }

    private void createTabs()
    {
        ActionBarSherlockTabBarPlugin.instance.setSherlock(sherlock);

        // You can either provide a text by string literal or resource ID (R.string.something).
        ActionBarSherlockTabBarPlugin.instance.addTab("tab-home", "Home", null);
        ActionBarSherlockTabBarPlugin.instance.addTab("tab-settings", R.string.tab_settings, null);
    }

    @Override
    public void onActionBarSherlockTabBarPluginInitialized()
    {
        // Now it's safe to access ActionBarSherlockTabBarPlugin.instance because the plugin was instantiated
        runOnUiThread(new Runnable() {
            @Override
            public void run()
            {
                createTabs();
            }
        });
    }

    // All setContentView methods are overridden because ActionBarSherlock has to modify the view
    @Override
    public void setContentView(int layoutResID)
    {
        // Don't call super!
        sherlock.setContentView(layoutResID);
    }

    @Override
    public void setContentView(View view)
    {
        // Don't call super!
        sherlock.setContentView(view);
    }

    @Override
    public void setContentView(View view, LayoutParams params)
    {
        // Don't call super!
        sherlock.setContentView(view, params);
    }
}

Set a compatible theme for the activity in AndroidManifest.xml. Predefined themes are Theme.Sherlock, Theme.Sherlock.Light and Theme.Sherlock.Light.DarkActionBar. You can define your own with Android Action Bar Style Generator. Note that the predefined ones must be prefixed like @style/Theme.Sherlock.

As last step, register the plugin in your config.xml:

<plugin name="ActionBarSherlockTabBar" value="de.andidog.phonegapplugins.ActionBarSherlockTabBarPlugin" />

Usage

Use the plugin like so:

<script type="text/javascript" src="ActionBarSherlockTabBar.js"></script>
<script type="text/javascript">
    document.addEventListener('deviceready', function() {
        actionBarSherlockTabBar = cordova.require('cordova/plugin/actionBarSherlockTabBar')

        // Note: setTabSelectedListener is the only exposed function at the moment
        actionBarSherlockTabBar.setTabSelectedListener(function(tabTag) {
            console.log('Tab ' + tabTag + ' selected')
        })
    }
</script>

See also the example project in the repository (note: you have to download and reference ActionBarSherlock yourself).