My upgrade success as an MVP was near-100%, although most of that flying was west coast hops from SEA/PDX down to SoCal or PHX/LAS. It's definitely worth requesting the upgrade every time as you never know who won't show up for their F seat. Your upgrade request will last all the way to the airport.

As mentioned, some upgrades are being requested automatically now. In some cases if the ticket is changed or reissued, you may need to re-request the upgrade, so be vigilant.

One of my favorite benefits of MVP was just being able to pick a seat from the "preferred" section up front. Even when the back half of the plane is completely full, often the seats up front are wide open and you can frequently still grab a bulkhead seat. Enjoy your new status!