It would seem that a Google engineer named Diane Hackborn (Wow! If that isn't the perfect name for a software/hardware tech engineer, I don't know what is!) got tired of all the confusion regarding hardware acceleration on the Android platform and decided to set the record straight and educate us all. She recently posted a long bullet-point style discussion post on her Google+ page with some great details on the subject.
A brief summary is that Android has always had some minor forms of hardware acceleration built-in; however, versions of Android prior to 3.0/Honeycomb didn't have GPU acceleration, but only CPU acceleration, which was far less efficient. Google introduced full graphics acceleration into Honeycomb, and it is "no more full" in Android 4.0/ Ice Cream Sandwich. The only difference between Honeycomb and ICS is that the newest version of Android adds a change in default settings so apps designed for the new OS will automatically activate hardware acceleration. You can check out her full discussion at the Google+ source link below.
Source: PhanDroid and Google+ - Diane Hackborn