Thanks!
The recursive triangle one is easier to understand, but this one's much faster as it doesn't repeat already drawn lines! 
Wow! Yet another way to draw it! The Sierpinski Triangle is the CS equivalent of proving the Pythagorean Theorem in math -- there are hundreds of ways to do it.
Your way is interesting because it doesn't actually draw the outside border; it's sort of a leaky gasket. :~) I don't entirely understand how it works--I'm going to have to spend more time with it.
Talking about speed: Snap! Build Your Own Blocks
Check it out in full screen for best resolution.
It just draws and fills a triangle, [then wears it as a costume and stamps it three times in a triangle shape], then repeats what's between brackets.
I think @dan_garcia was doing something like this with other fractals.
The only issue here is that the drawing starts losing crispness after iteration 8 or so, but it's cool and super fast nevertheless.
Wow!! this is soooo fast I can barely see it happening!
This is wonderful! It's the same idea as the "world's fastest fractal" I created some years back and showed at one of the Scratch conferences...
http://tinyurl.com/SnapWorldsFastestFractal
dan