Yep, the '+' as a separator is one of the many Postfix features.
However, the problem with using the "account+identifier" is that the identifier is simply ignored when delivering mail. With a real alias I can actually revoke an email address, by simply removing it from the aliases. With an identifier I would have to explicitly reject mails for a given recipient part.
I prefer to keep things simple. Bouncing spam is a bonus.
gam create alias idontwearseatbelts user crashtestdummy
The only problem with aliases is that it completely breaks using email as a unique id to link you with people. You basically fix spam but lose the "people you may know" feature on social sites where you actually care about knowing who you may know on it (i.e. not linkedin).
Explicitly reject / add a 'move to spam folder' filter, but yeah. And some places I've given +names have sent to my un-suffixed address (I mostly suspect bad email sanitizing / filtering due to Hanlon's Razor, but ya never know).
Later this +postfix makes it easier to find out which source is the leak.
Most of the websites let you sign up with "+" in your e-mail but unfortunately not every site.
The other trick is that GMail ignores "." in email user so my.name can be just as well "myname". Not that it helps with the spam, just a sidenote.