Netscape (IIRC) would do another GET (or POST!?) when doing a view-source, which NEVEREVER made sense to anyone I would demonstrate it it. I want to see the source of the page that's currently rendered, not the source of another POST request. That behaviour thankfully seems not to be present in any modern browsers.
I may be misremembering, but didn't NN also re-GET on RESIZE EVENTS? I'm sure there was a very clever reason for doing so, but it sure did piss me off at the time.