Apart from the Sony Ericsson Xperia X10, there are just two Xperia handsets (Xperia active and Xperia pro) that do not have a stable version of CyanogenMod. However, nightly builds for both of these handsets started in the last few days that could mean a stable ROM release in the near future. CyanogenMod right now is based on Android 2.3 (CM7), however they are also working on CM9 (based on Android 4.0) that will release when it’s ready.
If you’re unfamiliar with nightlies, think of them as rough CyanogenMOD builds that are released every night based on that day’s coding. Therefore, they are often untested and not meant for the average user. Expect them to have some issues and don’t expect to use it for daily use. If you’re eager to try them out you can get the Xperia pro CM7 nightly builds from here and the Xperia active nightly builds from here.