While the technical critique of fellow photographers can be useful, I would rely a lot more on the layman's opinion. Unless, of course, you are shooting test targets.

Most of what we contribute to a photograph is an opinion. Discussing the grammar and spelling can only get you so far; it's the opinion that counts in the end. As long as the technical aspects of your photography (the equivalent of spelling and grammar) are well-enough developed to allow you to express that opinion, then you don't need a bunch of fifth-grade grammar teachers going over your work with a red pen. That will tend to leave you with purely documentary work. You captured an undistorted picture of what was there. Yay! If forensic photography or shopping mall "portraiture" is your goal, then that's not such a bad thing. I guess.

The "correct" exposure, shutter speed/aperture/ISO combination used to get that exposure, lighting ratio and composition are all largely subjective. Getting them textbook-perfect is just a jumping-off point, much like learning how words are spelled and combined to form sentences and paragraphs is a jumping-off point for effective writing. Your subject is just a list of facts. You want to tell a story, and it is your story that is being judged. You may have to commit some informed grammar infractions to make the story more effective; you probably have to bend the truth a little, and sometimes even lie outright.

The problem with relying on photographers' opinions is that, while they can point out obvious technical flaws, they're no better at judging artistic merit than anyone else. In fact, they're often worse — not because they have no aesthetic sense, but because they're looking with a technical eye. That is a bit of an over-generalization. There are photographic communities (like the folks at 1x.com) and individual photographers who can see the big picture first, but in the online enthusiast world you're much more likely to find a community of competitive "experts" who will be looking at histograms, putting composition rule overlays on your image to see if you've exactly followed, say, the "rule of thirds", and looking at your pixels instead of at your picture. And that's great while you're learning spelling and grammar, but once you've gotten the basics down it's a little less than useful.

Laymen might not be able to tell you exactly what you need to change in your process to improve a picture, but they will be able to tell you what they like and don't like. And sometimes it may be the case that what is disturbing them is exactly what you were trying to accomplish. It's that reaction to the story you are trying to tell that matters.