I knew someone to attended WWDC this year so I myself believe it or not, tried it. I made a time machine backup and then reformatted and did a clean snowy install. Installation went very fast, about 15 minutes. First thing I did was install a CPU and RAM monitor on my menu bar to see how much better it was. I did my normal stuff and saw I was only using about 1 quarter of all of my memory. Before I would be right at the top, and sometimes getting the HDD involved.
It was an improvement, and all apps opened faster.
I really saw the performance when it got OpenCL in the equation, just looking at the temps on my computer, if my CPU was maxed out to the limit, so would my GPU. I noticed that video conversions went faster with this and overall the boot time was cut in half.
The only real features I saw were some extra dashboard widgets and you can change icon size on the fly with a slider in the finder window.
I downgraded because of the WIERD errors i was getting. if i can find some screenshots that i took i will post them.