Beside a rich features of Android Ice Cream Sandwich (ICS) that you can find on ICS spec., you might need to aware some QAs series that you will face after upgrading to ICS:

Q. Can I use Bluetooth 3.0 HS function in ICS version?

A. The Ice cream Sandwich OS feature does not support Bluetooth 3.0 HS (High Speed) function

However Bluetooth 3.0 is supported.
If you want to transfer a file at a faster data rate between devices, you can use Wi-Fi direct function. (where the other device supports this function)

Q. Can I see Adobe flash contents in web browser?

A. No – To view compatible Adobe Flash contents of a web page, please download Flash player from Android “Play Shop”” (Previously known as Android market).

Q. I use the exchange server account in my mobile and can not upgrade its OS to ICS through Kies.

A. Some exchange server account requires the “device encryption” to connect to
exchange server.

“Device encryption” limits the synchronization or firmware updating through Kies.

Please decrypt or initialize your mobile after data backup and try to upgrade again.

Q. Wall paper and Widgets after upgrading?

A. The Wall Paper set prior to ICS update will revert back to the “default” setting
The Widgets set prior to the ICS update will be initialized

Q. Application compatibility for ICS?

• Some 3rd applications will not work in ICS OS
• If so, please advise customer they will need to advise 3rd party application developer that an update to the app is required.
• Any way, today, most of the application support ICS that it might not so worried

Q. Khmer Unicode on ICS?

A. As I already stated in my previous post, Khmer Unicode doesn’t work natively on ICS controls or application like facebook, Google Plus or twitter as GingerBread that we at least see the character but with ICS, you will see blank.

But with browser of ICS, you can browse any website that embedded Khmer Unicode correctly with font embedded or Google Webfont, we don’t need Khmum Browser to view that.

Check detail in my previous post.

Any way, I haven’t experiment all of them, they are from other users’ comment and manual for Samsung Galaxy S2 with ICS.

Please share if you have faced other problems with Android ICS on other devices or Samsung Galaxy S2.