[eno_]

At the top of the table on http://neo.jpl.nasa.gov/risk/2004mn4.html, the most recent numbers are 2.2e-2, or about 1 in 43.

[SunkenCiv]

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