I have a boss with a very common last name - not quite as common as smith though. He has a "jsmith@yahoo.com" email address. He constantly gets emails meant for other j smiths.
Mostly it's an annoyance, and pisses me off that more places don't use double-opt-in.
I've had the GMail account since 2004 and I got no mis-addressed mail until at least 2008 or 2010, then only stray ones until about 2013 when all of a sudden there was an uptick and it seems like there must be at least 20 people who at least occasionally use my email address by mistake, at least on occasion.
I've gotten Alitalia boarding passes, tax data, all kinds of things. I'm on a family mailing list. I got a reply to someone who sent an email (using my address) from behind the steering wheel of a top-down Miata. Imagine their shock when I sent back an identical picture from behind the wheel of my own identical car.
Another good one was the kid who kept signing up for college information using my address. Then one day I got email from a college administrator saying the snail-mailed info packet was sent back to them as unaddressable, and asked him (me) for clarification as to his postal address. I politely pointed out that he also, unfortunately, provided an incorrect email address. I was thinking to myself "not everyone is college material", but others assured me I had done the right thing.