I have restricted who can create posts in the Announcements category. Please let me know if you would like to be able to post in that category but are not able to.
Announcements are intended for items of community-wide interest, and many of us have set up email notification of all posts in that category.
I have created a "Google Summer of Code" category in which everyone can create posts: "Use this category for general discussion on Google Summer of Code, including introductions and questions."