I know that whenever I fly, I try to give a pilot report for each and every leg that I fly. I sometimes check on DUAT to see if the PIREP has been published, and most of the time (9 out of 10) it is.
Often times, that unforecast weather isn't published with the PIREPS, but it is passed on to other aircraft in the vicinity. An example of this would been when you're flying in and around thunderstorms and turbulence. The controllers will often tell you what an aircraft 10 miles ahead of you is experiencing, and what you can expect!!