I will tell you whats Going on.
Kenya now is in a reconciliation phase because of the last elections held in 2007.
There are two main contenders/parties in argument where one party states that the other rigged the election process to win while the other states otherwise.
Anyway, all in all, measures have and are been taken at this moment to solve and contain this problem and only a few affected areas are raising concern which are the Western and Rift Valley areas of the country.
So if your travel plan was to visit the Mara, then you might as well as cancel your trip, for this month only, but after January ends, everything will be back to Normal. Also travel advisories just scare people into going somewhere while the real truth is that they should be capable of stating which areas are not safe.
Nairobi area, Eastern, Southern and North areas are as safe as ever.