Using HTTP cache headers effectively

Hi,

Some time ago , martin fowler bloged about how HTTP cache headers can be very effectively used in web site design.
http://www.martinfowler.com/bliki/SegmentationByFreshness.html

How actively HTTP cache headers are considered in web site design? I think it is a great tool to reduce lot of load on server and should be considered before designing any complex caching strategy. Thoughts?

Thanks,
Unmesh