In response to Kristina Killgrove's query on her friend's behalf, I'm happy to report that, in my experience, hiring committees are pleased to see evidence on your CV of "Professional and Public Engagement". These activities don't take the place of refereed publications, but they certainly do add value to your qualifications.
Professional Engagement/Activities refers to your service contributions to the profession, such as reviewing articles for journals, adjudicating grant applications, and election or appointment to offices in professional societies. Contributions to conference organization would fall into this category, too. Even if you're a grad student who is not yet contributing at this level, you should list any service that you provide to your students' association or to the student membership of your professional society. It is a good idea to separate these from public activities on your CV, although both normally would fall under the broad heading of "Service".
In the past, Public Engagement/Activities were limited to public lectures and interviews/stories about you that appeared in local/regional/national/international media (radio, TV, print). But the growth of social media and the reach of the Internet means that there are now far more ways for your research and/or teaching to be recognized. Definitely include these on your CV, but if you didn't author them they don't belong under "publications". You may need to be creative with category headings, but these could be as simple as "Media Interviews" and/or "Media Reports on my Research". You should include the title of the interview/story, and when and where it appeared. "Public Lectures and Presentations" is another useful heading.
Blogs should be treated differently. If you author a regular blog that is aimed at students and/or professionals in your field, I suggest that you provide a separate heading under "publications", titled "Blog Posts". Members of the hiring committee probably are not going to view the blog itself so you should provide a short narrative that describes the title and the nature of the blog (include the URL), along with a list of the last 5 or 10 posts (with titles and the dates that they were posted; call this "examples of recent posts"). If you have an impressive number of followers, include that stat in the narrative.
Even if you have contributed only once to a blog such as ProfHacker or GradHacker, or to other blogs that appear in the Chronicle of Higher Education, Inside Higher Education, or University Affairs (as examples), be sure to note it under the heading of "Blog Posts" or under a more general heading such as "Outreach Activities".
If you author a personal, rather than professional, blog, it doesn't belong on your CV; nor do "service" contributions that are unrelated to your professional persona. For example, coaching your daughter's soccer team doesn't belong on your CV. (Yes, I've seen this.)
Don't include reference to your Twitter feed in the body of your CV; if you list the URLs for your web site and your blog under your personal information at the top of the CV, you could include your Twitter handle there (but do so only if you tweet/retweet on professional topics; don't include it if you routinely tweet personal stuff).
Most hiring committees will be pleased to see that you take public outreach seriously (and, yes, evidence of outreach does help in tenure review). Just remember that those outreach activities do not take the place of serious scholarship. And here are two final notes of caution: 1) your colleagues may not be even half as impressed with your outreach activities as you are; and 2) do be aware that professional jealousy may rear its ugly head if you are something of a social media celebrity.