The ability to resize your brushes and change the hardness on the fly, rather than using the brushes dropdown dialog, is a HUGE time-saver. Talk about a great feature that I wish had been in Photoshop all along...
The only improvement I could suggest is to be able to switch between size and hardness on the fly, i.e. if I'm holding ALT to change the size and I add SHIFT it should instantly change to hardness. Having to re-right-click makes it difficult to switch from size to hardness or vice versa while keeping the brush in the same position.