Since 2005, Google has sponsored a “Summer of Code”, a program where students are given paid internships to work on open source projects. The program operates in a three-phase cycle. First, organizations and mentors submit proposals for their projects, then, students apply to work on the given projects. Finally, the two groups get associated with each other and so begins the coding.
On its Open Source at Google blog, the company has posted that they are now in phase 2, student applications. Students have until April 6th to go through the 180 accepted projects and submit their application.
Google is hosting an event on April 2nd to explain the entire process, but the Summer of Code website has quite a comprehensive FAQ section for interested students. A ball park figure of 1000 students would probably be selected into the internship program.