In my early days on the internet (1998) I opened an email account with one of the first free email providers in Italy (I couldn't speak English then). My account on www.libero.it was one of the first on that website, I think. I picked up a very simple username, mitika, and in the latter years it has become so popular that there have been a lot of mitika-something usernames on Libero. Not so seldomly I find in my inbox emails of registration to some websites, including username & password and a link to activate the account. With those datas I can access the website and surf in the other person's profile. If the other person put his/her credit card details, I could access them too.
Unfortunately I don't even know how to contact the other person to warn him/her about the mispelling of the email address which caused me to receive their subscription details. Now I just trash these emails.
This is avery curious thing since in the real life I have an unique surname (I think there are less than 10 ppl on earth with this surname and all of them are my relatives) and I never happened to be misconfused with someone else.