I do not think it is appropriate to post student e-mail on a blog for the purpose of ridiculing a student or telling the world how stupid or annoying they are. Many bloggers seem to feel differently. What justifies this kind of post? How would you feel if you came across a blog which posted a less than flattering e-mail you'd written (potentially under stressful and less than optimal circumstances in which you were subject to the authority of that person)?
Despite my own inner propensity for angsty venting, I agree with Mano. I'm all for generalized complaints about the newest manifestations of e-mail etiquette gone bad, but at the end of the day, I think charity begins at the keyboard. If there's an eighth deadly sin, it's probably Hasty E-mailing. As I explain to my students now and again, I refuse to discuss grades over e-mail in order to protect undergrads from their own worst impulses (of the "You idiot! How dare you give me this grade!" variety). But even I--more likely to worry endlessly instead of froth at the mouth--have been known to fire off nasty missives to, say, people who can't recognize obvious allusions to Jonathan Swift. In all likelihood, I wouldn't enjoy seeing those e-mails again...
When I started blogging under my own name, I decided that certain areas had to be off-limits. No griping about colleagues or administrators; no negative comments about students that couldn't be generalized to a group; no work-related complaints, except of the most frivolous sort. It seems to me, at least, that a non-anonymized blogger should use a public forum as the place of last resort for specific complaints, not the first--especially when students are involved. This is especially the case when the blogger doesn't intend to pursue his or her complaints through official venues (an appeal to the chair or dean, the grievance committee, the courts...); it's a trifle disconcerting to find someone howling about a Grave Malefactor, only to discover that the malefactor in question probably has no idea that the blogger is upset. Doesn't the Malefactor have the right to his or her day in court? Obviously, anonymized bloggers have more leeway in this area, although they're also more likely to risk their own privacy in the process.