I met my boyfriend at a bar. He came up and introduced himself to me while I was talking with my friend about him, considering walking up to him and introducing myself to him. I don't think I'll ever be looking again, but in my past single life, I was not opposed to introducing myself to guys. I had reasonable success with it, too.
As for the cashier situation... In college, my good friend was a cashier at a convenience store. She met her then future, now ex-husband there by ringing him up a few times. That's the only experience I know about that, and it didn't work out great in the end.