Nobody takes a cut of cash...
Come on, we wanna talk seriously? Then let's do it, even if that can sound a bit off topic for the question opening this thread.
Everyone knows that cash is not for being shipped inside a mail, no post service expressly allow you to ship money that way, you can't get any insurance for shipped money, so everything that happen to your mail (lost, destroyed, stolen) will be at your risk only. Even before web payment processors came out, for sending money anywhere post used money orders, that means the same sending money but no physical cash sent. Same thing for the money transfer services. So what's really the issue, the fee? I still think it's much better paying a higher fee (that btw will be paid by the sender) and being sure I'll get the money instead of getting a mail with cash wrapped inside.... also considering that mail wouldn't be shipped for free. If you compare the price for a registered mail to go abroad, you will see it's not that cheap.
Another issue can be privacy? Mail can be sent to a P.O. Box but web payments often need your real name? That's not true either. Many processors allow you just to choose a nick or an email account and your real data won't be shown to your sender.
Final issue can be taxes? Well, I think that nobody will piss off if you get occasionally some money and transaction is registered somewhere (if they will find out of course). And if you don't get money occasionally then I would strongly discourage you getting it in mails.
So my reply is still no, i never received cash in mail and I hope nobody will use that way for sending me money.