In addition to Eric's answer, I spent a lot of time on the right decision.
Remember that these elements must go in the parent theme of the application, inheriting from Theme.Sherlockor the like.
<style name="AppTheme" parent="Theme.Sherlock">
<item name="android:actionBarStyle">@style/AppTheme.ActionBarStyle</item>
<item name="actionBarStyle">@style/AppTheme.ActionBarStyle</item>
<item name="android:homeAsUpIndicator">@drawable/action_bar_ic_ab_back_holo_dark</item>
<item name="homeAsUpIndicator">@drawable/action_bar_ic_ab_back_holo_dark</item>
</style>
Do not put them in a custom action bar theme that inherits from Widget.Sherlock.ActionBar.
<style name="AppTheme.ActionBarStyle" parent="Widget.Sherlock.ActionBar">
<item name="android:icon">@drawable/action_bar_logo</item>
<item name="icon">@drawable/action_bar_logo</item>
<item name="android:displayOptions">showHome</item>
<item name="displayOptions">showHome</item>
</style>