gcc_select should probably "never" be used. The system ships with a
default compiler (gcc 3.3 on Panther, gcc 4.0 on Tiger and Leopard)
and that should probably "never" be changed. Software that needs a
different compiler should specify that explicitly.

Users who had used gcc_select to select a different compiler used to
experience all sorts of weird breakage with some MacPorts software.
Recently (1.5.2?), MacPorts was changed so that it doesn't matter
what the user has selected with gcc_select; MacPorts will use gcc 3.3
on Panther and 4.0 on Tiger and Leopard unless the portfile specifies
something different using configure.compiler. This is a good thing.

Apple's gcc 3.3 only builds PowerPC binaries, so it's not suitable
for use on Intel Macs.