I saw a blog from ZDNet on advice for students entering the workplace. It's good common sense, and I think it makes sense. The highlight, though, is the last item.
Keep your work and personal life separate.
That fits with what I talk about. Keep your personal blog, thoughts, Facebook, etc., separate. There should be some separation in your life, and I'd extend that to your brand as well. Make a separate blog, even a separate Facebook profile, for your professional world.
For students that don't have a profession, I'd plan one when you start looking for jobs. For me that was the start of my senior year. If I were entering my last year now, I'd go about it this way.
In August, I'd get a hotmail/gmail/yahoo email address that will remain constant for me. I'd be wary of my school or ISP accounts. You might move across the country in a year, and you want a fairly permanent address. This also allows you to build a separate profile.
I'd choose the places that make sense for me. Ask professors, contact others in your field, see where they tend to make profiles. Many people use Facebook. LinkedIn has done well in many technology fields, Ning seems to work well in Europe. Pick the one that works for you, create a new profile, note your professional items: your major, internships, etc.
Set up a professional blog. Include posts that are relevant to your field, things you've learned or worked on, projects, etc. If you have a personal blog with this stuff in there, copy posts over.
Use this email and profile, and blog, in your resume, cover letters, etc. as the place to learn about you and why you're a good employee.