Each writing community is different. When you're ready to post your fics, ideally you would look around and see what the place is like, and what you're going to get from the people in the community. Like with ff.net, you'll get a lot of reviews, but they'll mostly be of the (and I quote from a ff.net tab I have open right now) "great chapter" for every single chapter you write. If you look around several forums, you'll see the type of reviews posted there. Some fanfic forums (SPPf comes to mind) are known for giving a good amount of in-depth reviews, so if you want to improve your writing, you go there.
PC's fic community has always been rather quiet on the review front. So... =C