I tried CM9 Ice Cream Sandwich (Android 4.0) test build on my Samsung Galaxy S2. It is so cool, I loved it. It have some limitations.
See some screen-shots
– RIL crashes on providers with NITZ makes phone unusable
– RIL sleep issues
– low haptic feedback
– sensors aren’t working very good
– proximity sensor works, but is initialized with wrong state on boot
– Camera Parameters
– video recording
– some missing video codecs
– and a lot more
Remember if you are going to test it do it at your own risk.
If you want to read more and try this, check this thread on XDA Developers. Once again read and search and make sure you are ok to do this.