I love reading about LLVM internals. It's exciting to see LLVM still making major algorithmic improvements to something as important as register allocation- it's a really nicely designed library both to use and to work on, and bringing the generated code's performance closer to compilers like GCC makes it even better.
It looks like Omnigraffle, which runs on OS X. Given that llvm is mostly sponsored by Apple, I could imagine a lot of the devs are running OS X. I used a bit back in college and I remember the shadowed boxes looking like that. I especially liked it because it generates vector graphics for inclusion in LaTeX documents.
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 [1], then include them directly into my (pdf)latex source.
