I recently signed up with NASDAQ's Level II service, a service sold through money.net. As usual there was a request on the website for my email address. I entered nasdaq.level2.com@mydomain.com. Now that mailbox is getting spammed to hell. Either money.net's servers are not secure, or they are selling their subscribers' information.
I cannot stand these people. I had to have American Express stop payment to get out of their supposedly free trial after they charged me a month. This was after four unanswered emails to every email address I could find on their site trying to cancel only days after signing up. When they continued to charge me for a second month, I finally went into their site and made all of my account info garbled and that finally ended it. I like your approach of using a different email address for each site you visit. I do that myself and it works great.