as I noted, the NASA figure given for 2.2e-02 is 1:45...
http://neo.jpl.nasa.gov/cgi-bin/ip?2.2e-02
Impact Probability: 2.2e-02
2.200000000% chance of Earth impact
or
1 in 45 chance
...and as tortoise noted, now there are some more observations, and the odds of impact have improved a little.
http://neo.jpl.nasa.gov/cgi-bin/ip?2.7e-02
Impact Probability: 2.7e-02
2.700000000% chance of Earth impact
or
1 in 37 chance
or
97.30000000% chance the asteroid will miss the Earth
I just heard that Spacewatch has found some images containing the rock from March 2004, several months earlier than the official discovery. This will greatly extend the baseline, making a much more accurate prediction possible than what they have to work with now.
Maybe I should make this my tagline...
http://neo.jpl.nasa.gov/risk/2004mn4.html