In my experience, long compile times usually occur due to poor software engineering regarding the build.
For a good book on the subject, please read "Large-Scale C++ Software Design" by John Lakos.
For a good essay on just makefiles, please read "Recursive Make Considered Harmful" by Peter Miller, at <http://www.pcug.org.au/~millerp/rmch/recu-make-cons-harm.html>. Many makefiles commit two cardinal sins: 1) build too much (thus takes too long), 2) doesn't build enough (thus unreliable unless a clean-build is done, the usual culprit being failure to track dependencies).
Some tips:
NEVER include a header file that is not needed by the compilation unit.
ALWAYS include every header file required by the source or header files.
CONSIDER using header-header files, which contain a bare bones subset of a header file, primarily for other header files.
CONSIDER implementing the "pimpl" pattern (pointer to implementation), to help disassociate the implementation from the interface and reduce often unnecessary "cascade recompiles".
HTH, --Eljay
