Jan Freeman is one of the few professional language columnists who's much more interested in finding out about something than in bemoaning it. (Acutally, Russel Smith seems to have improved. He's still focusing more on style than language these days, but when he does take up a linguistic topic, at least he doesn't make an ass of himself like he used to.)
Freeman writes a weekly Boston Globe column called The Word, always worth a read. Now she's got a new blog.