When one businesses address starts getting spam I blackhole it.
Similar to the + suffix trick but works on any site.
As you point out, the ability to blackhole any of these one-off addresses makes the approach a great way to deal with spam and quasi-spam. It's a shame that so few people are set up with the necessary software or infrastructure, so it remains a bit of a fringe approach.
I particularly enjoy the reaction of some retail employees when they think, for a moment, that my e-mail address includes the name of their store. "Your email address is 'abcpeetscoffee'?" "Well, yeah, for this particular transaction it is."
Just make sure you renew the domain and maintain ownership. Even if the domain provider says they'll ensure ownership after expiration, I don't trust that they will. Assume the domain is ripe for new ownership by somebody else once it expires.
There are services like Mark Monitor which address this issue, but they are prohibitively expensive and only useful for large enterprise.