Three reasons why I favor using sentence case* (as opposed to title case) for blog headlines:
1. Sentence case is the trend in print and on the web.
2. It seems more credible and natural, like a person's voice. (Though, on the other hand, title case is more authoritative.)
3. With lots of blog newsreaders, all the prospective reader sees is the headline (before clicking through). That's why I favor (potentially) more provocative headlines, which are often sentences ("Want to overthrow your dictator manager?") in sentence case rather than labels ("Overthrowing the Dictator Manager") in title case.
Seth Godin’s blog usually illustrates the power of sentences and sentence case in blog headlines.
*"Making the Case for Sentence Case" is title case, meaning the capitalization follows the style used for book titles; "Making the case for sentence case" is sentence case, following the style for...you guessed it, sentences.