Yes this is also something that I should be doing, but then I also recognise that I am no expert and so giving unsolicited advice on other peoples' work can often come across harsher than intended. But I have given my opinion through in-depth critiques when asked :)
Interaction is a also a big part of it, not just critiquing or giving feedback. Conversations and that sort of thing, which I've not always been the best at in the past.
Ah well, such is life, even though I think it's more common for the other person to appreciate tips he/she is getting :) And I'm not saying it has to be critique, but maybe as good tips?
As I tried to help someone by commenting about aperture use only to notice, that he had only taken the photos with a phone camera and all his other photos (with a real camera) were far better than I'm getting.. well, mistakes happen :D