Rebelle shortcuts are the best!
It's been a year now that I've been using Rebelle (6 and 7) for most of my paintings and I love the way its default shortcuts work.
Wanna increase the brush size? Hold CMD + drag left or right with the pen/mouse.
Wanna Blend? Press 4.
Wanna Paint & Mix? Press 2.
It feels so natural to me now. Whenever I use other painting program I miss these conveniences.