My trial preferred experience
I purchased trial preferred in mid-June knowing I would be doing two transcon roundtrips this Summer. I've done two so far (PHL-PHX and PHL-LAS) and was upgraded to first on 3 out of the 4 and the 4th I had 10C on an A321 (loads of leg room).
(I was shocked I got an upgrade from LAS-PHL on a Friday, but am not complaining!)
Very happy. I qualified until Feb 2012 and will be returning to PHX sometime in October so that will be useful. I doubt I'll be able to keep it but I'll bunch my future trips up and buy it again next time I can.