Replaces Android Market, looks about the same and works about the same. Just with a new name and new WHITE icon.
I forced the update by going to Settings > Applications > Manage applications > All > Market, where I clicked on Uninstall Updates. After that you open Market, that will reverted back to the old one. Run it for a minute or two, then exit it the app and when you start it the next time it SHOULD update itself (if you’re online) to the new Play app.
It can later be found under all apps as Play Shop with a new white icon. And, if you look at it under settings and such to empty it it’s of course called Google Play Store now.