Footnote backreference with hyperref

Question

This question led to a new package:
footnotebackref

I'm using hyperref to have footnote marks link to the footnote proper and I'd like to have some sort of "backreferences" from the footnote proper back to where they're called (à la Wikipedia). For example:

This[1] is the text[2] that serves[3] as an example[1] to
the footnote[2] backrefence thing[4].
-------
[1] The first footnote. [a, d]
[2] The second footnote. [b, e]
[3] The third footnote. [c]
[4] The fourth footnote. [f]

Where a, b, c, d, e and f are links to the first, second, third, fourth, fifth and sixth places where footnotemarks are respectively.

I hope I managed to communicate what I'd like, I'm not that good at it :P

A MWE follows.

\documentclass{book}
\usepackage{hyperref}
\begin{document}
  This\footnote{The first footnote. [a, d]} is the text\footnote{The second footnote. [b, e]}
  that serves\footnote{The third footnote. [c]} as an example\footnotemark[1] to
  the footnote\footnotemark[2] backrefence thing\footnote{The fourth footnote. [f]}.
\end{document}

Answer 1

Edit: Using the new package footnotebackref

Just include the package in the preamble and use the \footnote-command as usual. There are two options which are described in the package documentation.

\documentclass{article}
\usepackage{footnotebackref}
%\usepackage[symbol=$\wedge$]{footnotebackref}
%\usepackage[numberlinked=false]{footnotebackref}

\textheight=3cm
\begin{document}\noindent
Text\footnote{The first footnote.} Text\\
Text\footnote[4]{The second footnote.} Text\\
Text\footnote{The third footnote.} Text
\end{document}

---

The original answer:

Here is a non tricky approach for the backreferences. I used the hyperref[target]{text} command from the hyperref package and created an new footnote to expand the standard footnote command. Before I set the standard footnote I place a label with an unambiguous(!) tag (myFootnoteTag) for the label-ref-mechanism using an independent counter. To reference the label from the footnote the hyperref[]{} command is used. This is set to the footnotetext and create a clickable reference in it. Here one can choose between different styles for the clickable item.

\documentclass{article}
\usepackage{hyperref}

\newcounter{myHyperFootnoteCounter}

\newcommand{\myHyperFootnote}[1]{%
    \refstepcounter{myHyperFootnoteCounter}%
    \def\myFootnoteTag{hfn:\themyHyperFootnoteCounter}%
    \label{\myFootnoteTag}%
    %\footnote{\hyperref[\myFootnoteTag]{#1}}% clickable footnotetext
    \footnote{\hyperref[\myFootnoteTag]{$\wedge$}#1}% Wikipedia style
}

\makeatletter
%clickable footnote number
\renewcommand\@makefntext[1]{%
    \noindent\makebox[1.8em][r]{%
    \mbox{\textsuperscript{\normalfont\hyperref[\myFootnoteTag]{\@thefnmark}}}\,}#1%
}

\makeatother

\begin{document}
Text\myHyperFootnote{The first footnote.} Text\\
Text\myHyperFootnote{The second footnote.} Text\\
Text\myHyperFootnote{The third footnote.} Text\\
Text\myHyperFootnote{The fourth footnote.} Text\\
Text\myHyperFootnote{The fifth footnote.} Text\\
Text\myHyperFootnote{The sixth footnote.} Text
\end{document}

Edit: After the question of Stephen I give an extended version. I use the TeX-command \@ifnextchar to branch between the footnotes with or without optional argument. If the next char after \myHyperFootnote is [ the macro \my@OptHyperFootnote will be executed. If there is no [ the macro \my@HyperFootnote will be executed. Keep in mind that all macros are in the \makeatletter environment now because I used the @ in the 'submacros'.

\documentclass{article}
\usepackage{hyperref}

%a new counter to create an unambiguous label-tag
\newcounter{myHyperFootnoteCounter}

\makeatletter

% branch between the footnote with/without opt. argument
\def\myHyperFootnote{\@ifnextchar[\my@OptHyperFootnote\my@HyperFootnote}

%define an new footnote without optional argument
\def\my@HyperFootnote#1{%
    \refstepcounter{myHyperFootnoteCounter}%
    \def\myFootnoteTag{hfn:\themyHyperFootnoteCounter}%
    \label{\myFootnoteTag}%
    \footnote{\hyperref[\myFootnoteTag]{$\wedge$}#1}%
}

%define an new footnote with optional argument
\def\my@OptHyperFootnote[#1]#2{%
    \refstepcounter{myHyperFootnoteCounter}%
    \def\myFootnoteTag{hfn:\themyHyperFootnoteCounter}%
    \label{\myFootnoteTag}%
    % put the optional argument to the original `footnote`
    \footnote[#1]{\hyperref[\myFootnoteTag]{$\wedge$}#2}% 
}

%if the footnote number should be the reference than redefine the footnote macro
\renewcommand\@makefntext[1]{%
    \noindent\makebox[1.8em][r]{%
    \mbox{\textsuperscript{\normalfont\hyperref[\myFootnoteTag]{\@thefnmark}}}\,}#1%
}
\makeatother


\begin{document}
Text\myHyperFootnote{The first footnote.} Text\\
Text\myHyperFootnote[4]{The second footnote.} Text\\
Text\myHyperFootnote{The third footnote.} Text\\
Text\myHyperFootnote{The fourth footnote.} Text\\
Text\myHyperFootnote[8]{The fifth footnote.} Text\\
Text\myHyperFootnote{The sixth footnote.} Text
\end{document}