Following up on this post, I exchanged some e-mails with Rabbi Dr. Asher Meir. In the meantime, he wrote two columns on the subject -- one available online here, the other to be released perhaps next week.
The following is what I gather from our correspondence, in my own words. Read it carefully, because there are all sorts of caveats. And keep in mind that Rabbi Dr. Meir has not approved this, so don't hold him responsible for it. I'm pretty sure that on one point, we both consulted with the same third party. This is intended to clarify the issues he raised in his two published columns on this subject (I, II).
1. One is allowed to discuss a neutral or positive story of public interest about any public figure by name (talmid hakham or not) without regard for potential denigrating comments. This is not the case for private citizens who probably do not want to be discussed in public.
2. One may discuss negative stories about general public leaders provided that one is certain that the stories are true (or adds appropriately worded caveats), one has no ulterior motives and one is not causing any harm to the individuals.
3. One must judge a talmid hakham generously and go out of one's way to give him the benefit of the doubt. Therefore, one must be extremely cautious in discussing negative stories (or stories that appear negative) about talmidei hakhamim.
4. One may respectfully disagree with a talmid hakham, even if others might take this as an opportunity to insult the talmid hakham.
5. One may review an article or book negatively. However, one should not be unfairly negative and should make sure to emphasize the positive aspects as well.