You've got your own domain. It's for personal use, so you've set up Google Apps to get free and effective email. What could possibly make this better?
The Google Apps Catch-All address, of course.
A Catch-All address is an email account that receives all incorrectly addressed email for your domain. If somebody typos your address but gets the domain right, the email winds up in the catch-all email account. The account owner will occasionally check through to make sure the email gets to the right recipient (If they type the domain wrong, they end up with a much bigger problem).
The catch-all address became less popular as spam got worse for fairly obvious reasons. Google, however, has remarkably good spam filtering, which gives us the option back.
What you can do with it:
You can come up with any email you like on the spur of the moment (say, SpurOfTheMomentEmail@yourdomain.com) and it'll reach your inbox. You can give a different email address to every person you meet and every site you sign up for and receive them all. It gives you an essentially unlimited supply of email addresses, because *@yourdomain.com is now yours. Hell, I sometimes use it to send subtle messages - If dave is hounding you for your email address, giving him email@example.com might get the point across.
Aside from the awesomeness and flexibility this gives you, it has some practical advantages - you can treat addresses as 'throw-away' email accounts. If a site sells your address on to spammers, you can just blacklist all mail to that address with email filters (shown below).
Setting it up:
Assuming you've already got a domain and set up google apps, it's very, very simple. If not, you may want to start at the beginning.
Log into the Google Apps control panel, and choose Settings followed by Email. Under the catch-all email section, choose to forward it to your main email account.
Save, and that's it. If you look under your account settings, you now have *@yourdomain.com listed as one of your addresses.
Blacklisting one of the addresses you gave out is easily done under your email settings. Click on Filters and then Create a new filter. Type the email you want to blacklist in the To: field, and hit Next Step.
Now simply check the Delete it box and click Create Filter, and that's it! Any future messages sent to that address will be silently moved to the deleted folder.
Now enjoy the freedom that only an infinite supply of email addresses can give you.