@d Same here. And I actually switched to it from writing longer paragraphs, because you might base that paragraph of text on some wrong assumptions or the one you are sending it to might not be interested in it at all. Splitting it to sentence-per-message is a great way to avoid that.
Writing longer messages works for blogs and e-mails, but not for IM, I do like longer replies, but I choose what's best for the medium I use.
@annika