I am batting around 75%, but I only buy cheap seats where I have a
reasonable chance of getting the UG, otherwise I will book J from the
get-go.
Last month, took wife and kid to FLL, had 1 J seat booked in advance and
wanted to UG the other two. We got the upgrades on the outbound, but
not on the inbound.

However, I just booked some trips to/from Asia, and took advantage of the
fare re-alignment by booking in M class ( new Tango plus) and confirming
the UG immed with the 2009 certs - saved me a few thousand dollars.