I think people dislike it because it's not as efficient. Lion takes a while to startup everything where you left it, sometimes I wonder if I would have been better off to close it all and open it with the time it takes. It's getting better though.
Lion takes a good 3-5 minutes to start up from cold to having restored my windows, due to all the disk thrashing it does loading all the programs back up at once. I get the feeling it doesn't often respect my choice of not opening the windows, so I get to sit there and watch it grind away opening programs I probably don't want it to open as that's the reason I rebooted in the first place.
It seems Lion's implementation of restarting apps depends on SSD type speeds. Also a fairly fat application like a browser has an entirely different amount of work to do before it stops loading compared with the very thin media players that this BeOS demonstration would have been demoing. Apples to Oranges, but BeOS's being multi-thread-mandatory from the start where Lion's application resume was an add-on feature to mature apps will make the difference pretty glaring.