How often should I run CHKDSK?

Since chkdsk fixes filesystem issues, it should not be nececessary to run it regularly unless you are encountering situations which might cause your filesystem to be corrupted (e.g. computer shutting down improperly, programs crashing while accessing files, etc.). This is especially true since Windows will detect if your filesystem has issues and will run chkdsk on boot if needed.

Theoretically, since NTFS has a slew of improvements, including journaling (where it writes down what it's about to write before it actually does it), much more advanced structuring, and most importantly, self healing (Slide 19). So no, chkdsk is virtually obsolete.

Once a month is enough. Now defragmenting is a different question altogether.

There are no recommendations on MSDN that I could find for recommended intervals to run chkdsk. I work in a small IT department as a programmer and I have never known anyone that ran chkdsk on a schedule. Personally I only run it when Windows suggests it. I do still run Disk Defragmenter on a semi-schedule. Running chkdsk on a schedule should not cause any harm, but as it can take a very long time to run on large volumes I would not do it unless I actually suspected something such as a disk failing.