Sadly this is at best a complicated workaround, that will will work for people that are motivated enough to remember for each different service a separate email and password and additionally to this you have to remember as well the credentials to manage your email address and check the emails from different sites.
In my case it would mean having about 100 email addresses.
You actually don't need separate emails for this. You can use (email@example.com, Gmail supports it and others too I'm sure). Or you can use your own domain (Google Apps makes this really trivial) and have the part before @ be the sitename (that's what OP suggests) and then have catch-all address. You might receive slightly more spam if you turn on catch-all, but I have a setup like this a it works.