The stock heatsink-fan is just as the coolers included with other retail Sandy Bridge processors, which the design itself has not deviated much in years since the inception of the LGA-775 socket. The cooler is sufficient for running at stock speeds and is fairly quiet. With the Core i3 2120 not having an unlocked multiplier (that's only for the SNB K-Series CPUs), the overclocking abilities are extremely limited, so this heatsink should do the job. Later on in this review are some thermal and power consumption results when using the stock Intel HSF.
If you are interested in the /proc/cpuinfo output for the Core i3 2120, it is available from this OpenBenchmarking.org log file. It's CPU family 7, model 42, stepping 7.
The Intel Core i3 2120 support under Linux is just like any of the other Sandy Bridge CPUs and it's been the same story for months. The Intel Core i3 2120 will work under Linux assuming you are using the very latest software components. If you are intending to use the integrated processor graphics, you will want the Linux 2.6.38+, Mesa 7.11, and xf86-video-intel 2.15.0 and later. However, as there have been a number of bug-fixes and performance optimizations, the most ideal situation is Linux 3.0, Mesa 7.11 / 7.12-devel, and xf86-video-intel 2.16.0. Ubuntu 11.10 is in good shape for SNB Linux graphics. If you are not concerned about using the Intel HD 2000 graphics, using Ubuntu 11.04 "out of the box" should work just fine in terms of compatibility with the Cougar Point motherboards and other areas of the system.