The CNJ section gives a great overview of the daily commerce taking place on the forum, it has shown me in a glance who is selling what and what the masses of people feel about the transaction.
I find that to be one of the first areas I read when I get to CPF, it gives a good indication of what is transpiring elsewhere on the forum. I agree that throwing out a cheers for something as simple as a purchase can be redundant, but if that information gathers enough momentum it helps to build a persons reputation, and provides an outlook for the newbies scanning the boards for their first (and never last) purchase.
I for example only visited this forum to find a deal and save a few bucks, it didn't exacly work like that though /ubbthreads/images/graemlins/broke.gif /ubbthreads/images/graemlins/icon3.gif.. I did get the deal I was looking for, then found ten other lights I couldn't live without. Even now prior to making a purchase I scan the CNJ, it's like word of mouth advertising in a mute world.