The update is rolling out in several European countries and South Korea as we speak, either over the air or through Samsung Kies. If you're unlucky enough and have not yet received the update, here's the instructions on how to flash it manually - so easy even I could do it.
Sadly, Samsung has managed to botch this update severely by, you know, not actually updating most of the user-facing applications. The TouchWiz launcher and lock screen are easily replaced (Nova Launcher and WidgetLocker, in my case), but the default applications are not. You'll be looking at the same Gingerbread-inspired TouchWiz dialer, contacts, music, calendar and SMS applications and system settings, with virtually zero changes. None of them integrate with ICS in any way.
Worse yet, the notification drawer and status bar do not integrate either, making those, too, look horribly out of place. However, thanks to this man's wonderful work, you can use CWM to flash the stock ICS notification tray and status bar over the Samsung ones. I did it, and it looks fantastic. The included My Files changes are pretty damn awesome, too, so be sure to install that one as well.
I'd love to replace the TouchWiz dialer, contacts, music, calendar and SMS applications with the stock Ice Cream Sandwich applications as well, but I have no idea how to do do something like that (help appreciated!). It infuriates me to no end that Samsung would rather shove inferior Gingerbread applications down our throats than just include the damn stock applications which are better in every possible way. I'd also love the stock Android keyboard, but the TW keyboard is actually pretty good, so that's not a big problem.
In any case, hopefully this means the source code release is underway, so we can see CyanogenMod 9 shape up quickly.