Nevermind, \parskip is a rubber length, so the effect isn't uniform.
> What do you think about the following (requires the verbatim package):
>
> \newcommand{\zzTop}{\vspace{-2\parskip}}
> \newcommand{\zzBot}{\vspace{-1\parskip}}
> \newenvironment{tightverbatim}
> {\zzTop\verbatim}
> {\endverbatim\zzBot}
>
> I'm also thinking about putting a -1\parskip between theorems and proofs.
>
>