Nelson Minar has a nice, short writeup of the Linux kernel bug that caused servers to spin out of control yesterday. Most initial write-ups blamed Java, but that was incorrect. Interestingly, Java not only accounts for leap seconds, but also mentions them prominently in the documentation for the java.util.Date class:
Although the Date class is intended to reflect coordinated universal time (UTC), it may not do so exactly, depending on the host environment of the Java Virtual Machine. Nearly all modern operating systems assume that 1 day = 24 × 60 × 60 = 86400 seconds in all cases. In UTC, however, about once every year or two there is an extra second, called a “leap second.” The leap second is always added as the last second of the day, and always on December 31 or June 30. For example, the last minute of the year 1995 was 61 seconds long, thanks to an added leap second. Most computer clocks are not accurate enough to be able to reflect the leap-second distinction.