As you may have heard, the poobahs who run the internet, to the extent anyone does, have gotten together to put all pornographic sites into one domain class, .xxx.
What you may not have heard is that a clever pornographer could take your domain name, if it might look good with a .xxx on it in place of the .com, and lift all the particulars. Your customers might be surprised. If you want an example of this, look at whitehouse.gov vs. whitehouse.com.
Fortunately, one domain registrar, Go Daddy, has published rules for acquiring .xxx domains to protect your main domain name.
The link is: http://support.godaddy.com/help/article/5789.