[topquark]

In addition to the two LIGO sites, there is the Virgo instrument outside of Pisa, Italy, which will come online later this year. The KAGRA detector is currently being assembled underneath a mountain in Japan. And, mentioned in another reply, LIGO has the equipment for a third detector. This is currently in storage in the hopes that the Indian government will build a facility. By 2023 there should be five widely-spaced detectors worldwide.

The resolution of time-of-flight between the two LIGO sites for the signal we just detected was about half a millisecond. This resolution is somewhat dependent on the signal strength and the location of the source relative to the detectors. With three sites we can localize most sources to tens of square degrees on the sky. This is still very large; the moon is a quarter of a square degree.

The odds are pretty good to observe only one event in 16 days of data, and the likelihood of seeing the event on the first day is the same as the likelihood as seeing it on the last day. The analysis of the remaining data from the first observing run (ended Jan 12th) will probably take a couple of months.