Also, check out Damaris Sarria's related post, which includes more details on the two interview periods.
In summary, NASA received 3535 applicants and expects to choose 120 interviewees with a target class of 15-20 astronaut candidates. Assuming 15 are selected, the selectivity of this NASA class would be 15/3535 = 0.4% (120/3535 = 3.4% interviewed, 15/120 = 12.5% of interviewees selected). Compare that to past astronaut classes in the figure below:
Also, based on past selections, we can expect the 2009 class to consist of about 12 male and 3 female with 9 military and 6 civilian.
Although it's extremely difficult to be selected as a NASA astronaut, it's even harder in Canada and Europe, where there are also current astronaut selection processes underway. Canada's CSA had 5352 applicants for only 2 spots, while Europe's ESA had 8413 applicants from 17 countries for only 4 spots. Japan's JAXA also received 963 applicants this year for only 3 spots. (Thanks for the info, Curt and Takashi.). Added together, this means there were 18,263 applicants from the US, Canada, Europe, and Japan for only about 24 spots (0.1%).
Thanks to an email from Curt on the Astronaut Hopefuls listserv, we learned that there were over 700 people disqualified due to medical, educational, or professional reasons. Thus, the pool of Qualified Applicants is approximately 2800.
Again, an email on the Astronaut Hopefuls listserv sheds some light on the process. Instead of 400 Highly Qualified appplicants, NASA chose 450. NASA apparently broke the applicants up into groups based on discipline and had selection committees choose the Highly Qualified people within each disciplinary pool. We have learned that pilots are last in this sequence, so their reference and medical pre-screening letters have yet to go out.
Reports are that the total number of applicants was 3564 rather than 3535.