I'm looking for new machine for FCP X, considering rMBP but heard about ghosting problems with screens. Any rMBP users having these problems?

It definitely is a problem ... but only on some of the panels.

Check out the Apple site forums. Just search for "Ghosting Retina" and you'll see what I mean.

I don't see the need for the Retina MBP. I have a 2011 MBP. Get a 2011, cheaper, and there is no benefit to the Retina imo. Especially for editing.