It is a phrase that has recently come across, to describe a type of male, who...is straight, but is fashion conscious, "image" conscious (i.e. spares no expense for facials, manicures, ect...), and particulary into vanity.
In short, doesn't like to get his hands dirty.
There are "feminine" qualities in him (a sensitive side) as well as straight, masculine sides. I believe there have been recent articles about the phenomenon, but I cannot recall specifics (read one a couple of weeks ago in the local Tribune).
A "metrosexual" is a regular "Oprah" kind of guy.
Livius, can you add to this?