There will be a leap second June 30 2015 at midnight UCT. FSMLabs has tested TimeKeeper on Red Hat Linux and found that TimeKeeper handles the leap second properly.
TimeKeeper avoids using the mechanism for managing the leap second that is sometimes built into Linux. By default TimeKeeper “slews” on the leap second to allow a gradual resynchronization over a few minutes. This “slew” cushions the effect of the Leap Second on applications and insures that time does not go backwards.
The Linux component that compensates for the leap second is quite complex and has a history of causing system crashes.
Using TimeKeeper means that you don’t have to worry about the following issues (the following text is copied directly from Redhat’s note: Resolve Leap Second Issues in Red Hat Enterprise Linux. Emphasis is added.