I use +, so username+domainname@email-vendor.com

Which is in the RFC, but yet the sheer amount of times I sign up for something. Like a bank, or a financial firm, get the confirmation e-mail, and then click "Verify your address"

And get HTTP500 as their SQL has kicked up a stink

(The RFC also allows for (recursive (comments, so there's probably a middle ground between insanely overengineered specifications and a )))regex( someone found on a PHP forum somewhere (and yes this post is a valid email address (assuming there is a local regex account (or alias)))