I can't speak for all PS legs, just the one I'm most familiar with LAX <-> JFK. I'm 2P (will be 1P soon and for 2010), and have gotten upgrades for all 8 legs in 2009.

Will be doing the trip again this coming week, and right now my flights show C9 and F8. Seat map in Y looks almost full. C seat map looks almost full. F seat map is empty except for 2 seats. My upgrades to C using CR1s were confirmed well over a week ago.

Every time I take these legs, the flights are sold out, with standby for Y, so clearly they UG members with status to make room for more Y pax.

The only seats I know are reserved for 1P and above are rows 5 & 9 in C cabin.