I just read on www.cyanogenmod.com that CM9 (Ice Cream Sandwich) has been marked as stable.
Technically speaking, there haven't been many changes between the latest nightlies, release candidates and the now tagged stable version. Most improvements have already been made over the past months and in my opinion it could have been called stable for a while now.
As I'm writing this post, the stable build for Samsung Galaxy S2 (GT-I9100) is currently ongoing, as this screenshot shows:
The CM developers now mainly focus on the new CM10 (Jelly Bean). There is already an experimental build for the SGS2 out, but there are still too many bugs to use it (for example no sound at all).
If you aren't running CM9 yet, give it a try! Here's how:
Step by step guide how to install CyanogenMod 9 on Samsung Galaxy S2