$ ./configure
$ make
$ make install
...use this version instead:
$ ./configure
$ make -j n
$ make install
The n in the second line is the number of jobs you want make to start. So to reduce compile time, replace n with the total number of cores in your Mac.
[robg adds: At some point, I'd like to test this with a large compile, but I haven't had the time as of yet. If you've done any testing on compile time reductions versus cores used, please post your results in the comments. I think this should work on multi-core G5s and all the Intel Macs...]

