Hey man! Sure I don't care, I've borrowed it from a bunch of different artists anyway.
For my thumbnails I usually start off with a palette knife which you can get if you search Barontieri's brushes in google. I personally think better in shapes rather than line. Line comes later when the overall shape is established.
For the environment/header, it's a technique called lassopainting. You basically use the lassotool in photoshop and draw with it and fill it (paintbucket or gradient etc...) and work with it that way. It's nice to get some more interesting shapes. Of course it'd be easier if I could show you. But google concept on mac on deviant art. This guy does a lot of lassopaintings he's figured it out a lot more than me. He also has some video's up etc. So definitely check him out.
Hope this helps at all and if you have any other questions let me know!
PS:sending a personal message it says my answer was incorrect for the given question?