If you are a new member and you have 5 or less posts. If you post a message that contains a URL or certain spam related keywords then your post automatically goes into moderation. Once its there either me or one of the mods need to approve it before it is displayed.
I've had it set up this way since we upgraded and its eliminated 99% of the spammers that register, create one or two posts with their link and then leave never to be heard from again.
So if you're a newbie and your post didn't immediately display, this was probably the reason why.