Acer previously announced April 27th as the day that Iconia Tab A100 and A500 owners would be able to get their Android 4.0 update, but it didn't go entirely to plan — while the release sprang early for the A500, the A100 update hasn't made its way out to everyone yet. That may well change for you today, though, as several more users on the AndroidCentral forums are reporting that they can now update their devices. You should be getting a notification saying that the Ice Cream Sandwich update is available, but if it hasn't appeared yet then it might be worth a manual check.