Can you tell me what settings you used for the pen? I use SAI as well, and so I was just wondering, because I've always wanted to be able to have the sharp, jagged outlines like that instead of rounded ones.
I'm using the settings has up on her dA. Not sure if I'm going about it the same way, though. Basically I make swift strokes (bound to be inaccurate, so plenty of ctrl+z going on) and then clean up the excess after every intersection. TONS of erasing going on.
Took a little bit, but I got used to mine fairly quick. The big work area definitely helps I'm sure.
Also, if you want to get sharp lines but don't have a tablet you can always use curves or the polygonal lasso tool in GIMP to get a similar effect. My last three submissions are the only ones I've used a tablet on, actually. Everything else is all mouse.
Well, I've been using the curve tool on SAI for my works, all with the mouse, but yeah... Um, I can't exactly remember what tablet it was, but my friend has it with him right now, so I'll see when he can get it back to me...