Google announced the timeline for the 2013 program today: http://www.google-melange.com/gsoc/events/google/gsoc2013
The ASF has applied as a mentoring organization in the past. I assume we will again this year. If so there would be a limited number of slots for Apache, which mentors (volunteers that lead the GSoC project) in individual projects to fill. My recommendation is to *not* wait for an ASF announcement calling for proposals, but to start thinking about possible projects now. My guess is we'll need to have proposals ready before April. So this this is coming sooner than you think. I mentored a student in the ODF Toolkit project last summer, so feel free to ask me what is involved. Regards, -Rob