Save time when compiling with microtype

Recently there was a discussion on the MacOSX-TeX about compilation time with the microtype package. Under some circumstances (particularly when using latexsym), very large increases in compilation time were seen with microtype enabled. The full solution was given by Robert Schlicht, the maintainer of microtype. In the end it comes to adding these few lines after loading microtype:

 \usepackage{microtype} \makeatletter \def\MT@register@subst@font{    \MT@exp@one@n\MT@in@clist\font@name\MT@font@list    \ifMT@inlist@\else\xdef\MT@font@list{\MT@font@list\font@name,}\fi} \makeatother