I have read about users who are receiving someone else's mail. They have some account that has been set to forward mail. It then appears that either (a) Google assigns the address to someone else (perhaps due to inactivity) or (b) someone else keeps inadvertently typing this email address. The mail gets forwarded to some other user.

If this is true, this calls the whole notion of "Gmail security" (and more generally large third party email provider security) into question. Now think about all the changes Google makes in the name of "security". One misspelling or typo and it is all for naught. The mail is sent to another user.

Does it really make sense to use a free third party email provider like Google for important purposes. It seems like we are making identity theft even easier (not to mention online ad services). One thing we know is Google will not discourage use of Gmail for important matters linked to a real identity. They want more personal information, not less. Meanwhile Google discourages automated creation of accounts not linked to real identities, which would be safer if compromised.