"Default" portgroup?

[Ken Cunningham]

Does there exist a portgroup that might be considered "default", ie port code that would be included on all ports installed on a given machine?

If not, it could be useful to have machine or system-specific portfile additions that would apply to all ports on a given machine -- like adding the libsnowleopardfixes code to 10.6 systems, or adding -stdlib=libc++ to the CXX directives on all ports with libc++ added, or other things that I haven't considered yet..

Ken