The goal is to upload pictures, showcase them, and most importantly, to exchange critiques. The site has several tools to help you do this:
Before being able to upload any pictures, you must indicate the kind of equipment you are using. On the one hand, users experience this as "customization" of their profile, and on the other hand, this provides interesting information to data miners.
You can put "email alerts" on three of your pictures for free. Whenever somebody posts a comment, you will be alerted. If you want more email alerts, you need to become a paying member. This is a tried and true way of making money: Withhold a convenient tool from non-paying users. If you are not very active, then this doesn't hurt. Just offer one or two pictures every now and then for critique, and use email alerts for the latest pictures only, assuming that the old pictures won't get any more comments anyway. If you are very active, however, you'll start to feel the need.
It is difficult to have a discussion if you can't tell if anybody is following up on your comments, however. There is a crude way to do this: In your workspace, you can list all the comments you made. The comments are linked to the appropriate picture, so by following the link, you can then check whether anybody followed up. I don't think the owner of the picture would actually send you private mail in order to discuss the comment you left on his picture.
The community is so big that a "recent changes" mechanism would be overwhelming. On the other hand, all the important new stuff is pictures. Thus, the solution is easy: Just display a random selection of the pictures newly uploaded pictures. This works very well.
If you are interested in receiving feedback, this random appearance on the "recently uploaded" list is the default way to attract attention to your images. The next step is to ask for critiques. One last way to receive feedback is to critique other peoples' pictures. Your username on the comment will be linked to your "homepage" on photo.net.