It rocks. One of my biggest problems when I was drawing in Flash was dealing with wobbly and uneven lines when trying to do the line art, but SAI's Pen tool nips that right in the bud. I'm still relatively new to it myself, but it has already knocked out on of my biggest problem areas in art.
Cool thanks guys I'm definitely going to give SAI a run.SAI is great for lineart, such smooth lines!! And I just can't deal with photoshop, I dislike how weak the blur tool is and the lack of the watercolour tools. And I have never used Flash, I thought it was mainly for animating?
Yeah, GIMP is a great starting program~ And SAI is beautiful, if you enjoy digital painting but want to have the feel of traditional painting, then go for it! Plus, you can get much smoother line art with SAI, as well as more editing options for each brush/tool.