In our experience a lot seems to depend on the agent if going with a Virtuoso agent. We had a former Virtuoso agent who processed two trip reservations for us and then we never heard another thing about it; upon check-in the upgrades were not available on arrival. I didn't think much about it at the time, despite knowing better in retrospect that occupancy did seem low. We had no personal relationship with that agent, I think she was just randomly assigned when we contacted Virtuoso back in 2004 regarding a trip.

We switched to DavidO last year after so many on flyertalk recommended him, and since then upgrades have been available on all three reservations we booked with him. Actually, if my memory serves he contacted me on at least one trip ahead of time and told me we had already been upgraded. And on another reservation the upgrade was substantially more than a one-category upgrade, and he has been able to work out a late check-out when needed to fit with our flight schedule. I can't say if it is coincidence or not, but our upgrade success has certainly improved when David has made the reservations.