Acer not too long ago decided to let folks know their Android 4.0 ICS updates for the 7-inch A100 and the 10.1-inch A500 Tabs were well on their way. That said, Acer noted the A500 wouldn't see the update until April 27th in the US or Canada, yet some folks in the forums have already got their OTA update sent out to them.
If you have a Acer Iconia A500, go ahead and check for updates -- you may find it there waiting for you. If you're looking to find out what all the changes are, head on into the Android Central forums where some folks having been going through the update. While most stuff seems intact, notably missing is the Acer added ring which many appreciated on the device but was an Acer customization.