There are many of us out there with Android devices that have hardware buttons, and are a bit concerned whether or not an eventual ICS update will stop the functionality of those buttons. The folks over at Gizmodo took the liberty of asking Google directly, and from their report, we do not need to worry. A Google representative had this to say,
ICS does have onscreen buttons but not always. If there's a device with hardware buttons the onscreen buttons won't be there, and the hardware buttons will act and function as you'd expect them to.... back and home will function as you'd expect, the search button will query the search bar (as you'd expect), and the menu button will query the menu overflow in the action bar.
Google did indicate that it won't work on some older "legacy" devices, but most folks do not need to worry about having useless buttons on their phone. Whew! That's a bit of good news.

Source: Gizmodo