Beamer: footer with current slide number but not total slide number

You can redefine set the footline beamer template in a way similar to the original definition in the file beamerouterthemeinfolines.sty, but suppressing / \inserttotalframenumber:

\documentclass{beamer}
\usetheme{Warsaw}
\useoutertheme{infolines}

\makeatletter
\setbeamertemplate{footline}
{
  \leavevmode%
  \hbox{%
  \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,center]{author in head/foot}%
    \usebeamerfont{author in head/foot}\insertshortauthor~~\beamer@ifempty{\insertshortinstitute}{}{(\insertshortinstitute)}
  \end{beamercolorbox}%
  \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,center]{title in head/foot}%
    \usebeamerfont{title in head/foot}\insertshorttitle
  \end{beamercolorbox}%
  \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,right]{date in head/foot}%
    \usebeamerfont{date in head/foot}\insertshortdate{}\hspace*{2em}
    \insertframenumber\hspace*{2ex} 
  \end{beamercolorbox}}%
  \vskip0pt%
}
\makeatother

\begin{document}

\begin{frame}Test\end{frame}
\begin{frame}Test\end{frame}
\begin{frame}Test\end{frame}

\end{document}

In case you really just want the slide number and nothing else, I found the following solution to be really easy & flexible:

\makeatletter
\setbeamertemplate{footline}
{
\tikz[overlay]{\node at(12,.25){\thepage};}
}
\makeatother