While I've been avoiding my listservs until I finish reading Harry Potter and the Deathly Hallows, I did see a couple of e-mails regarding J. K. Rowling's use of punctuation. What people were talking about was Rowling's use of run-on sentences in this particular book. They said she was frequently using commas where she should have been using periods.
I'll say. Over and over again you'll find complete sentences joined with a comma instead of separated by a period. Colons and semi-colons are used to separate/join sentences, too. I think I'm seeing more colons and semi-colons while reading this book than I've ever seen in my life.
I don't recall seeing this in the earlier Potter books. I'm not passing any judgments here, folks. (Given my own sporadic comma use and fondness for incomplete sentences, that would be foolhardy.) I'm just making an observation.