I found this question on Answerbag: "What is the highest count recorded by a bacterial pure culture in LB medium" on 11:34 PM, December 22. Now, this could be a question someone asked for their own curiosity or for an argument, but it sounds like a homework question. The fact that it was posted at 11:34 PM, too, sounds like someone was in the middle of doing homework.

Could someone call up their local (academic or public) library at 11:34 PM and receive help for this question? No. Even if the local academic library is open, which increasingly it might be, the librarians and/or library students aren't paid anywhere near enough to be up at odd hours and circulation staff isn't going to be able to help you. Students in New York could theoretically call Hamilton Library at 11:34PM NY time and get reference service, but no student is going to think of that. Their only option, if their school offers it, is to use a chat system.
UH-Manoa offers a 24/7 not very well marketed chat system that has "over 100 participating libraries". However, it advises "For in-depth help, you may wish to contact your subject specialist." As someone who's done general reference, I'm not sure I would be able to find an answer to the Answerbag question above. So not only would you have to find the chat reference link, which is perhaps buried on your library's website, you would have to feel comfortable chatting to a complete stranger who might not even be able to give you the best reference because they might not be a specialist.

Then, this student may head to the web and to a Social Q&A site. I won't elaborate too much on the structure of these sites since we all were on Answerbag, but like Leibenluft says, people tend to get credit for simply posting an answer on Social Q&A sites and the answer isn't necessarily correct. I think we all saw a few snippy or funny but not qualitative answers get huge numbers of points on Answerbag. It is possible for a student to get a correct answer from an expert who is browsing the site, but not always.
Leibenluft favors Wikipedia over a Social Q&A site because Wikipedia entries are edited. But besides the traditional information literacy arguments against the online encyclopedia, Duguid pulls down Wikipedia's usefulness by illustrating how one detail can throw off the coherency of an entire article. Either way, I cannot think of a substantial way for libraries to use non-internal wikis, so I will move on to Social Q&A once more.
Here are the problems I see with reference service in the current library system, and where (sometimes) Social Q&A has libraries at an advantage:
1) Library websites are not equipped for mobile technologies, as discussed in Dempsey. (Most social Q&A sites aren't either.) iPhones can load regular websites, but it requires moving the screen's focus to see the entire page which I found tiresome. A text-only mobile friendly page with the most frequently needed pages, including a "Text a librarian/chat with a librarian now!" function would help.
2) No personalization of reference:
Students like asking for help from librarians they are already familiar with (Dempsey, again). For the librarians' health it is probably better that they are not available 24/7, but in an ideal world subject specialist librarians would be accessible by some sort of message board system and by text message (school-provided number).
The student-librarian relationship could be encouraged further by a personalized login page. When a student logs in, the system would link the classes that student is taking to the broader subject and, along with providing related resources, could give the name and contact information of that subject librarian.
3) People like the "bulletin board" format of the Social Q&A.
Dempsey discusses the decisions libraries have to make about social networking technologies: does the library build its own software, wait for tech companies that make software for libraries to make the software, or jump on someone else's software? In the most dramatic course of action, libraries could pair with Social Q&A sites to have a "Expert Answers" section - where only librarians could post answers, and they would get paid to do this. Libraries would then cross-link their site to the Social Q&A site, and make the librarians answering have visible profiles (but not too specific, so not to raise privacy concerns) so that they can become familiar to the students. In a less dramatic version, libraries could implement their own bulletin-board type Q&A with the institution's own librarians answering anonymous or profiled questions.
This solution takes the "Social" out of "Social Q&A", and does leave the task of getting the information up to the authority. Individuals have a real need for specific, accurate information - like the question about bacteria up there - and due to a number of issues, including personalization and bulletin board formats, the only online reference service libraries offer (chat) is not pulling in many of the users with serious information needs. Then, they go to Social Q&A sites or Wikipedia, and receive information that may be correct, but probably isn't.
I wrote this post as pertaining to libraries, since that is my specialty, but you can see what libraries have on Social Q&A sites - authority, sometimes specialty, and often years of experience searching the web/books/databases for The Right Answer.