I wrote a while back about the SGS II and ICS coming to it. Well a month later, things have moved quite significantly. First, Samsung announced and started deploying their final ROM based on ICS. I am saying based since the feedback is fairly bad and having tested it myself, I can report that it is slugish and not really nice. It feels like a rushed version of a beta. It of course contains touchwiz which destroys ICS’s looks, which for me is a no go.
In the Cyanogen territory, some fairly good news have come around, nightlies are now build when the changelog is big enough and I can only say that it improves over time. Latest build is really fast, video codecs now work, a newly improved stock kernel is in the works to do better than Samsung, Cyanogen also announced their take at security and many other things coming (Trebuchet).
Last, I would suggest taking a look at the CM9 discussion thread on XDA which contains all you need to know to flash the device. Keep in mind this is experimental, so take a look at the FAQ before coming back crying, and yes, there are issues (though that list decreased a lot over the last month). I would also suggest you try different modems depending on where you are and your usage, until recently LPJ worked quite nicely for me but LP6 seems to save more battery, you can find them all here. The ROM is experimental but honestly, this has now become my permanent ROM, I have no motivation/blocker to go back to CM7 (Gingerbread).
As of the date of this post, Samsung sources are still missing in action…