I actually really like facebook messages (except for the security issues); I tend to use them for social messages with my facebook friends (which is essentially a superset of my real life friends). I use it to message my girlfriend (tied with iMessage) about "when do you want me to pick you up from work", etc.

(The obnoxious thing is that both of our phones are Verizon iPhones; there's no simultaneous voice and data, and unlike me, she tends to do long voice calls with people. I'm trying to get her to switch to a SIP client, so we can do G.722 wideband and crypto/vpn on the voice too, and non-extortionate international long distance.)

You can have them forwarded to real email, which doesn't announce that it's been read.

Why do you want to hide that you red the message ? Is it when you would like to ignore the sender but are too curious and would like to know what message he sent you ?

Yes you can. That is a feature that is completely able to be turned off.