However, I am frequent reader on PM (strange for me) mostly because community is great and feedback system (up/down vote) is so valuable that I would really missed it in NNTP-like client.
Well, the technique is there
, although it's mostly used to filter spam. Potentially far more useful than the (IMO) worthless XP system we have here. Feedback is useful if you can use its results - to ignore posts for instance. But here you can only find out the reputation of a note by voting for it - and hence, spending more time on it than you want.
Usenet clients usually have a much better "feedback" system than Perlmonks has: the ability to score articles based on their headers.