Y2K IS A BUST: NOTHING HAPPENED (MUCH): After all of the hype (or perhaps because the hype inspired the programmers to get busy fixing things), there were no serious computer problems from the Y2K "bug". A few glitches were seen:
@ A US spy satellite was sending data that the Pentagon could not read for three hours due to a Y2K problem in the ground station. The problem was solved (after two days of only limited data); the satellite itself was never affected. The Pentagon declared this to be the "one significant incident" of Y2K. [The Pentagon would not tell what kind of satellite this was, but insisted that it was not a missile warning satellite.] The Pentagon later admitted that some of the data sent down by the satellite had been "lost forever" due to the problems in the ground station.
@ A cash register at a PX in Okinawa could not process receipts. There were a few dozen cases in which a computer worked just fine but was putting the wrong year (1900) on printed documents.
@ Nuclear power plants functioned normally, although some support systems stopped working. These included four stations that lost access to weather data for a few hours, one clock that controlled non-critical systems had to be reset, a "monthly trend" chart was disrupted for two minutes, and (at Russellville, Arkansas) a computer system that tracked the movement of personnel in and out of radiation-controlled areas briefly failed.
@ The Oak Ridge, Tennessee, Y12 nuclear reactor (which makes the material for the MX missile warheads) suffered a Y2K breakdown, but this "did not affect operations or workers". The exact nature of the incident was not released as everything at Y12 is highly classified, but the glitch had not been fixed by 5 Jan.
@ The expected "massive assault" by hundreds or even thousands of computer hackers was nowhere to be seen. The Pentagon did detect and block four attacks by hackers on its web sites.
@ Japan confirmed that the Y2K bug had triggered six minor faults at nuclear power plants, three of which affected operations (but not safety). All have been fixed. At Onagawa, a sensor to monitor sea water temperature sounded an alarm after its clock jumped to 2099. At Shika, the system to monitor radiation and temperature stopped working after its clock jumped to 2099. At Fukushima, the position of a control rod could not be displayed because three clocks had jumped to 2036. Three record-keeping programs (two at Fukushima and one at Kashiwazaki) failed after their clocks could not display the correct date.
@ There were minor problems in software that handled various support functions in one Spanish and two British nuclear plants. 
@ NASA reported "minor anomalies" including a disrupted set of planning software. Spacecraft and communications continued functioning without incident. Computers on the new space station were shut down ahead of the changeover but restarted without problems after it was over.--Stephen V Cole