Ours is a community divided.  The Great Orange Satan himself and various other front pagers, such as Kagro X, entitle their postings using the sentence case convention, that is, they capitalize their titles as if they were sentences.  Others, such as openthread, mcjoan, Hunter, DarkSyde, DemFromCT and SusanG, use the title case convention in which all "important" words are capitalized.  Still others (brownsox, I'm looking at you) allow some hidden variable to dictate the style.