Since this has not been answered yet.

#1 you click on someones name, which shows their profile
#2 at the bottom is trust, which opens the trust page [1]
#3 at the bottom of that page you can leave positive or negative feedback. Its intendet for trading, but I occasionally use it to remind myself that I dont want to deal with certain people here. There is a lengthy part about it in the unofficial faq [2] if you want to know more.