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.