There were a series of earthquakes starting at 10:13 JST yesterday (2007/07/16). The epicentre was in Niigata Prefecture (新潟県), where the larger quakes reached 6-upper on the Japan Meteorological Agency seismic intensity scale (if that sounds just like the Wikipedia article, don't worry, I am only plagiarising myself).
Down here in Tokyo, it was only a shindo 3, so our experience was summed up by the JMA as follows:
Felt by most people in the building. Some people are frightened. Dishes in a cupboard rattle occasionally. Electric wires swing slightly.
As I said, people in Niigata were not exactly OK; 7 dead / 790 injured, according to the Daily Yomiyuri. Also, there was a fire at a nuclear power plant; from the same article:
The Nos. 2, 3, 4 and 7 reactors at the Kashiwazaki-Kariwa nuclear power station in the prefecture automatically shut down after the earthquake, according to Tokyo Electric Power Co. A small fire broke out in an electricity transformer of the No. 3 reactor, but no damage was reported to the reactor. The fire was extinguished at about noon.
Google News info: http://news.google.com/news?as_q=niigata+earthquake&svnum=10&as_scoring=r&ie=UTF-8&oe=UTF-8&tab=wn&resnum=0&ct=property-revision&cd=1&btnG=Google+Search&as_epq=&as_oq=&as_eq=&as_qdr=&as_drrb=b&as_mind=15&as_minm=6&as_maxd=17&as_maxm=7&as_nsrc=&as_nloc=&as_occt=any