Here are the statistics on the earthquake near Lee Vining today.
The earthquake occurred with the following parameters:

26MAY2001 11:59:03 PDT 37.986N 118.760W ML=3.9 SCSN 20 mi E of Lee Vining, CA

SEE:
http://quake.usgs.gov/recenteqs/Quakes/quakes0.html

The area described in Petra's prediction of May 11, 2001 has seen 79
earthquakes with Ml between 3.8 and 5.4 (her predicted magnitude
range) since 1931, slightly more than one per year. A number of these
have been immediate aftershocks, however, and the total number of
days on which an earthquake in the magnitude range has occurred in
the past 70 years is 49. The last earthquake in this geographic
range and magnitude occurred on July 22, 1999 (Ml 4.0), so in the
past year there have been no earthquakes and in the past two years
(since May 26, 1999) there have been two such earthquakes that
would have matched Petra's predictions.

Using the past two years as a background rate, the odds of choosing
a particular day for the earthquake would have been 1 in 365. If she
had chosen a window of up to 15 days, including May 26, her prediction
would have been statistically significant.

The earthquake actually occurred 14 days after the prediction date.
The probability of such an event occurring within 14 days after
the prediction is about 0.04. This is normally considered significant
in statistical terms.

Using the past 70 years as background, the daily probability of such
an event is about 0.002. For statistical significance she would have
had to predict the event within 28 days of it's occurrence.

I should point out, however, that Don and Petra revised their
prediction after the non-occurrence of the Lee Vining earthquake
during 11-13 May, 2001. Their new prediction was posted on
May 15 as follows:

Magnitude: 2.0-4.0
From: 05/19/2001 - To: 05/25/2001
Location: Mammoth Lakes
Lat: 37.5N - Long: 118.7W - Range: 32

Today's earthquake was about 45 km north of this predictive
region and one day too late, although the prediction was matched
perfectly by 6 earthquakes of Ml>=2 in the area on May 23-24 and
one of Ml 2.8 on May 21.

Let's say Don and Petra had given a radius of 50 km and taken
the largest event they proposed with a 3-day window, which is essentially
the window above, but centered on the 23rd. Then what are the chances
of hitting today's event, which would be a match for all parameters
for this slightly revised prediction.

In this case 3 earthquakes have occurred in the past year in this
geographic and magnitude range on 3 separate days. The probability
of such an event on any given day is about 0.008. In a 6-day window
the probability would be about 0.048. This is a statistically
significant result (although just barely) (assuming the magnitude
range Petra gave in her initial prediction).

By pure guesswork, Petra could have predicted her Lee Vining
earthquake on any of 26 unique 14-day periods during the past
year. She would not have had the satisfaction of seeing the
Lee Vining event on any of these 26 tries. The one time she
did chose to post her prediction, however, the 14-day period
after the prediction did in fact, see a qualifying event in
the Lee Vining area.

I think a little Champagne on Memorial Day is called for Don -
if you plan on seeing Petra over the holiday, celebrate, it's
not every day you have a near miss (or a success for that matter).