Tagging a user in a post
If you are familiar with Facebook and/or Twitter, you may like this feature. If you want to "tag" another user in your forum post, you can simply type his/her username with an @ symbol in front of it. After you submit your post, the user you tagged will be sent an alert that you tagged him/her, with a link to the post.
For example, I can tag Angel by simply putting [USER=100]@Angel[/USER] in my post. So I might want to post something like this:
Hey, I bet [USER=100]@Angel[/USER] would like this thread!
You will notice that after you type the @ and a few characters, after a brief delay it will show suggestions in a list under the text. You can select one of these and it will automatically be completed for you. Anyway, give it a try and you'll see what I mean.