make has a -j option for using multiple processors. Now most of the machine have more than one processor, it would be a waste not to use it.
The best way is to let fink automatically use -j <n>, where n is the number of processors, as a first option to make (so that scripts can override it if they think they know better).
As a proof of concept, I use:
/usr/bin/make.orig: <original make program>
#dirty hack to speed up fink
/usr/bin/make.orig -j 2 $*
And this does indeed speed up the process in the compilation phase, and does not appear to break anything.