This year, 2009, showed we need at least the following for GSoC:

Let all together define the goals, verify the goals, in a group and revise them where needed
Idea proposals should be filled out in full so that goals can be concrete before we let students pick them up.
~~A GSoC list where students can interact with the community as not all projects fit to internals and other existing lists~~ done. gsoc@lists.php.net && http://news.php.net/php.gsoc
A mentors list so mentors can exchange information without having to send mails with a longish CC line
Motivate more discussion between the different projects
Questionnaire during the application time for anything PHP specific, not everything can be handled by the generic GSoC form.
Weekly Reports to the GSoC list so all know what's going on
1. One org (don't remember which) has a nice approach sending weekly reports to the mentor only till midterm, project-wide after midterms

Links to other orgs

Python has a nice page explaining “What we expect”, a good read, http://wiki.python.org/moin/SummerOfCode/Expectations
Tor has a template for applications https://www.torproject.org/gsoc#Template
Etherboot has an overview page on the wiki and individual project pages where the student lists useful things like timezone, weekly journal entries and any project notes. http://etherboot.org/wiki/soc/2008/start
Advice for mentors, interesting info and links http://code.google.com/p/google-summer-of-code/wiki/AdviceforMentors

Two Weekly report template

Subject: XXX's Report for the two weeks starting: 2009-MM-DD

TIME SPENT: XX hours (approx)

KEY GOOD VIBRATIONS

< things that you were really pleased with >

KEY CONCERNS

< anything that is outside of your control and which 
  concern you >

WAITING FOR…

< if you are waiting for someone else in order to complete
  one or more tasks >

KEY TASKS THAT STALLED

< if something stalled that is not outside your control
  in and by itself, even if it was outside factors that 
  delayed it >

KEY ACCOMPLISHMENTS

< list as many things as you wish, but prioritize
  by putting the most important items first >

DETAILED ACTIVITIES

< This section is optional -- list here all minor tasks that
  did not fit into any of the categories above. >

MY TODO

< The major tasks you will be doing in the next couple 
  of weeks >