diff -r 9ea10b1adfaa -r 3781b30c4e2e text/intro.tex
--- a/text/intro.tex	Sun May 08 22:15:11 2011 -0700
+++ b/text/intro.tex	Tue May 10 18:08:26 2011 -0700
@@ -96,6 +96,9 @@
 
 The relationship between all these ideas is sketched in Figure \ref{fig:outline}.
 
+% NB: the following tikz requires a *more recent* version of PGF than is distributed with MacTex 2010.
+% grab the latest build from http://www.texample.net/tikz/builds/
+% unzip it in your personal tex tree, and run "mktexlsr ." there
 \tikzstyle{box} = [rectangle, rounded corners, draw,outer sep = 5pt, inner sep = 5pt, line width=0.5pt]
 
 \begin{figure}[t]