Summary: Many pros use this software. A great selection of tools and colours and a fairly intuitive interface make it a very useful. I use it to sketch prior to importing into Manga Studio EX when doing comic related work. If you can get it on sale I think it is worth it! ArrOOoo!
Summary: Sketchbook Pro 6 is my 'go-to' program for sketching backgrounds and characters (from rough to clean), and when combined with a Wacom Intuos or Wacom Cintiq, it is a robust and indispensable tool designed for productivity and flexibility.