Not OP, but I do the same thing using wildcard addresses on a domain I own. I might use hn@my.domain for Hacker News, amzn@my.domain for Amazon and so on.

Foregoing the custom domain, some email providers also let you add tags to your address (e.g. your_address+tag@gmail.com). I'm aware of some people who use that functionality to have unique email addresses for each service.