Since the release of the Ice Cream Sandwich source code, developers have been working fast and furious on ports to other devices. While the work should still be considered alpha at this point, it’s hard not to be just a wee bit giddy about all of the progress in this short of time. With the Galaxy Nexus not arriving until early December, these ports give us hope that relatively stable versions will be available on or around the Galaxy Nexus release.
The custom build of the Ice Cream Sandwich ASOP for the Nexus S is available at XDA. Use at your own risk and reward. Report back your results in the comments, if you make the move to ICS.
just wait until you can dual boot iOS5 & ICS