I have a similar issue with my personal domain, as an unfortunate number of in-duh-viduals in Utah seem to be unable to correctly transcribe the letters S F C N (for Spanish Fork Community Network), and instead enter S T E N. As a result, I receive email from educational, financial, government, medical, religious and retail organizations intended for specific Utah residents. In many cases, the senders are uninterested in the fact that the email is not reaching the intended recipient.
Personally, I report most of the messages as spam - they are unsolicited by the actual recipient (me), and if the sender cannot be bothered to confirm if the messages are being sent to the intended recipient, they deserve whatever trouble they have with their service provider.
Turning off the catchall feature is not an option, as I create far too many unique email addresses to set up on the server. Also, I do not use my own account name or the company name in the email addresses - once the address has been compromised and sold, the end recipient will have very little information as to what the address was used for. What I would like to do is find a provider who will do wildcard hosting, so I can use a catchall for *@*.STEN, blackhole any of the those hosts which are found by spammers, and severely limit the legitimate addresses @STEN.