This is pretty neat: Google Docs, which I’ve mentioned here before and increasingly trust, now features a drawing app. It seems to be pretty full-featured, although it doesn’t seem to have scaling and measurements. By full-featured, I mean, compared with Powerpoint, not with Illustrator.
Google Drawings is also (in my testing) a little buggy, but (in my experience) web apps get updated faster than desktop apps. Anyway, there it is, for what it’s worth. Your mileage may vary. You can export your drawing in number of popular formats, and they look pretty good to me. Here’s the PDF I exported from the above drawing.