Know it well (sigh). I have three domains registered to me, and all three are blessed with spam being sent using them as the forged origin.
What happens is that someone with your address gets a virus; their address book finds its way into various spamlists and you start to get spam.
Then, a spammer decides to pick your domain as his forged origin, and attaches all sorts of imaginative bits in front of the @ - I get stuff bounced back to
[email protected] as well as to
[email protected].
There's not a lot you can do about it, other than treat yourself to a spamcop account and route all your mail through it.