Some interesting stuff here: http://www.youtube.com/user/DreamworksAnimation/videos?query=tutorial.
The thing I notice is all these drawing tutorials are done in Photoshop. I've also noticed Nicktoons job postings for storyboarders and backgrounders where they emphasize your Photoshop skills.
So I guess the moral of the story, boys 'n girls, is the studios look for people who can draw in Photoshop. It's more cumbersome than SketchBook Pro but there are a bunch of tools uniquely available to you in Photoshop: masks, gradients, great transformation tools, superior selection tools (allowing you to modify and fine tune your selections), layer grouping...etc. etc. etc.
If Photoshop is too expensive for you... and soon it will not be available as a separate download, you'll have to subscribe to the whole Creative Cloud enchilada (http://www.adobe.com/products/photoshop.html?promoid=JOLIW)*... you might want to look into Corel Painter (http://www.corel.com/corel/product/index.jsp?pid=prod4030123&cid=catalog20038&segid=78&storeKey=us&languageCode=en).
I own Painter 12 and I'll be honest, I don't enjoy it as much as Photoshop or SketchBook Pro. However, it has its own version of most the Photoshop tools. It's good stuff but, in my experience, a little harder to manipulate. But that might just be me.
Painter 12 is software for people who like hardware. That is to say... it's supposed to digitally mimic the actual experience of painting and drawing in different medium. And it is true... you can produce works that really look like they were produced in oils, or chalk, or watercolor, etc.
I don't use it all that often but I intend to keep it updated... and I'll buy into any future versions. Hey, as a registered owner I should get a price break.
It doesn't cost anywhere near as much as Photoshop so, overall, it's something to think about.
Here's something else to think about. One way to break into Painter 12 so that the experience doesn't seem overwhelming is to first buy ArtRage. Extremely affordable and I have seen people do some amazing things in ArtRage. Get used to ArtRage, decide whether you're ready for Painter 12. But if you're going to buy Photoshop better do so quick... because that product is only going to get a whole lot more expensive.
*By the way, if you - like me - think compelling a subscription to Creative Cloud so you can use Photoshop is a bad idea, here is one way to make your voice heard: Eliminate the Mandatory Creative Cloud Subscription Model