centering frametitle in beamer

To center a frametitle (or subtitle) in beamer, simply add this code:

\makeatletter
\long\def\beamer@@frametitle[#1]#2{%
\beamer@ifempty{#2}{}{%
\gdef\insertframetitle{
\centering{#2\ifnum\beamer@autobreakcount>0\relax{}
\space\usebeamertemplate*{frametitle continuation}\fi}}%
\gdef\beamer@frametitle{#2}%
\gdef\beamer@shortframetitle{#1}%
}%
}
\makeatother

Thanks to this thread for this neat solution.