like tj said it's been discussed a zillion times but now that you've bought it up….
i had a go on maverickboys yesterday, i was well impressed, only on the road mind so didn't get a proper feel for any extra weight on the back end and didn't want to bounce mboys bike up the kurb. on saying that, i held the wheel on it's own and was surprised at the lack of weight, don't forget it replaces the mech and cassette at the back.
shifter works in reverse (11 speed will be the right way round) and you do have to ease up on pedal pressure to change, on the road this took about 200 metres to get used to, not sure about the dirt but hopefully will find out soon.
gear change is slick and dropping down the gears whilst slowing down or stationary ready for a start from rest is a real plus point that i didn't think would be of any benefit until i used it.
i'm sold on the idea, will be waiting for the 11 speed though as i want the extra range, on saying that crc are knocking 8 speeds out for £150 which sounds a proper bargain.