Well PE and the friend at casino analogy is quite flawed. The label that PE applies to players is based on a large database of statistics and is therefore likely very accurate.

Your friend's opinion of other players at a casino may or may not be valuable. It really depends on your friend's knowledge, etc... Even if he is a good player he may not know someone is a shark, depending how often he plays someone etc.... So it is much more imperfect information

Also I heard, and I don't have any solid info on this just something I heard on this forum, that PE (or one of those type of software types) will take your personal stats out of the database if you are a customer so other PE users can't see your rank but if you are not a customer you are screwed. If you ask me this is the WORST part of it, as it is essentially extortion... sign up with us or we are gonna stick a label on you for everyone to see.