1- It must (at least in some small, tangental way) be about writing. It can be about inspiration, art in general, creativity, but if I can't see SOME connection back to writing, it kind of doesn't fit here.
2- It must not be an ad. I don't care if it's a site that HAS ads or if the site is designed to create awareness about a product, so long as that is not its primary content. It's hard to come up with objective guidelines. I'll know sketchy when I see it. A tiny list of writing tips with eight inches on every side of scrolling banner ads would not be posted but someone blatantly promoting their book among a useful article about writing, I would.
3- It needs to be ABOUT writing. There are tons and tons of awesome places online to publish fiction or prose, and I even put some of my own stuff up, but for now I'm not ready to adopt the logistics that would be involved. (Though I might publish a writer-conscious piece of metafiction if the mood strikes me--especially if it's really funny.)
4- If I reach a point where I have more links than I can possibly post, I'll have to choose between them. I put up between half a dozen and ten links each Saturday, and I have hundreds of back up links. If I'm getting dozens of links a week, I will never catch up. Sometimes I even have themes in potpourri. That means I'll have to pick the best, most relevant and most enjoyable links I can find. It doesn't mean I didn't like something you sent me or even that I won't get to it eventually; it just means that with limited space, I had to pick the best fit.