As told before, I have the ICS as provided by Samsung (to it is not the stock ICS, it is the Samsung-version of ICS) on the Galaxy Tab 10.1. Now that it is nearly two months of using it, I want to share a little bit of my experience.
Basically it just works. If you know ICS already, you more or less know how it is on the Galaxy Tab 10.1.
The calendar app is different, it is the Samsung app, not the native ICS one. I have a problem to sync it with the exchange-connector as it is in Horde 4, but I did not take the time to investigate the issue. My Nexus S connects just fine, so it must be some modification by Samsung which is causing the issue.
Sometimes the tablet hangs, and I have to shutdown by pressing the power button for some seconds. This only happens when connected via WLAN. When I start the tablet again, it will hang again if I am not fast enough to enter the PIN of the SIM, unlock the screen and to deactivate the WLAN. But even then it will hang after the deactivation of the WLAN. After rebooting the second time (with WLAN already deactivated), everything works again.
The email app is also stuttering sometimes. This happens when I open a folder with a lot of emails and the email app is trying to determine if there are attachments or not. Either the app is not multi-threaded, or it is not well done.
Apart from that it just works.