Re: I've seen a definite uptick in these
The username+something@domain is called plus-addressing and has been available in sendmail (among others) since before gmail was a thing.
Don't try claiming that it's a unique gmail feature.
I don't think poster was, specifically, although the wording could be interpreted as though it's a Google mail only feature.
It's a good tip, that I'm sure there are more than a few that pass by here don't know about.
I recall reading about it (sendmail docs) years ago, I didn't know Gmail included it.