Quote - [...] Somehow this does not seem right, or even polite [...]

 

I would respectfully disagree. The username is what that person has chosen as a way of representing themselves here at this site, and if they choose not to reveal their true names, I think it's very polite to address them by their user name as a show of respect for that choice. If a user supplies their actual name, for example by signing a forum post, I accept that as an invitation to use the real name.

I admit it can be awkward, particularly when you don't know the gender of the person you're addressing or referring to, but I think it's quite polite.

You may call me Jack, BTW, if you like.