csquotes: wrong kerning?

It is not csquotes fault, it is a problem in the OT1-fonts: The kerning is missing if the quote symbol is entered directly and not through a ligature:

\documentclass{article}

\begin{document}

of''
of\char"22
of\textquotedblright


\fontencoding{T1}\selectfont
of''
of\char"11
of\textquotedblright
\end{document}

So this is another reason not to use OT1-encoding -- at least if you want to use the computer modern fonts (the lmodern fonts e.g. don't have this problem).

You can fix what ot1enc.def does (which is, in my opinion, wrong):

\documentclass{article}
\usepackage{csquotes}

% ot1enc.def has
%\DeclareTextSymbol{\textquotedblright}{OT1}{`\"}
% fix it
\DeclareTextCommand{\textquotedblright}{OT1}{''}

\begin{document}

\noindent
\enquote{nature of}\\
``nature of''
\end{document}