The default font, drop shadow, and line spacing are not exactly the same (suggesting that these figs may have been created using e.g. Omnigraffle), but it's easy to make something that looks pretty similar.
Not trying to be a shill here, I just think Powerpoint (07 and onwards) is underrated as a figure creation tool. I use it for all my academic papers, and have found it much less painful than Visio, Dia, xfig, and others with nice-looking vector (PDF) output. I don't know if there's a way to make Powerpoint do this out of the box, but I always throw figures through pdfcrop , then include them directly into my (pdf)latex source.