I used the beta for a month and purchased the final immediately.
The Basic Panel has some major upgrades to it - ACR7 is fantastic.
I also find I use the Local Adjustment Brush "Shadow" feature a lot too.
For me, everything else was icing on the delicious cake...
its essentially 50% the price of Lr3, which is also exceptional software.
Download the 30 Day free trial of Lr4 and decide for yourself.
just purchased and waiting for my link