Some of our newer members get a little bit confused when they make a post and it doesn't initially show up, so we thought we'd give you a little bit of a heads up on why...
As our membership grows, our board becomes more and more attractive to spammers. These spammers pay people in third world countries to sign up accounts and post messages for them. There are also some programs that can post messages automatically, but we've done a good job of stopping those. On the other hand, it is impossible to initially tell the difference between a human who has been hired by a spammer and a good honest member who wants to post useful questions or information.
As a result, we have designed a bunch of "red flags" that you can raise when posting as a new member. Among the ways you can raise these is by posting links or using language that is similar to the stuff that ends up in your spam email folder. When you trigger one of these flags, your post goes into a queue to be moderated and a moderator is notified that there's a post waiting. This prevents the vast majority of the membership from having to deal with adult content, sales pitches, or other inappropriate content - instead, the moderators just zap them as they come in and approve the appropriate stuff.
Sometimes it can take us up to a day to approve them, but usually far less. Note that if you make a post that doesn't trigger any of those flags, it will go through immediately.
After you've proven yourself as a non-spammer (we can't divulge exactly what the criteria for that is so that it's a little harder to work around), we open your account to allow those 'suspicious' posts to go through without hitting the moderation queue.
Hopefully this sheds some light on why some of your posts are disappearing if you've only been here a short time and/or don't post a whole lot.