@Celestial-Fox - I've never used SAI, Photoshop I've used a couple of times but I'm terrible at it :L
you should try gimp first, I used to use it before switching over to photoshop. Its pretty good and easy to use. Its a good program to begin with. Once you get better, then you can move to photoshop C:
^ Okay I downloaded it yesterday but haven't had a chance to use it yet, I'll probably sketch some stuff and mess about with it then :)
Also, those of you thinking that you can't get custom brushes on SAI, you actually can. And they're awesome brushes.
Heres a pack thats very nice:
Also, the coloring feels so much more natural, and you can blend colors alot easier than photoshop. It's actually more like Corel Painter, if anything. It's just a great program, and the linework can look fanastic. But if you do go ahead with buying it, it's good that you have gimp. SAI is quite minimalist, and GIMP will be cool for adding effects/editing and stuff.