ArtBoard does a lot of simple drawing functions. It seems like it's designed to appeal to kids & dabblers, and it does a great job at that. It is obviously made to be fun & creative, and I really liked it as a simple design tool.
But I was looking for something a bit more robust, that would output to SVG files, and ArtBoard only outputs to bitmap files. Which is great for kids & dabblers, but not for any serious design work.
I eventually bought iDraw because it exports to SVG. However, I was very disappointed in iDraw, since it is extremely limited, with only basic draw functions. It has a very rigid, unintuitive interface that can't be customized at all & has very few shortcuts, making even simple jobs tedious.
Then I discovered that the NeoOffice suite (the open-source app that rivals MS Office) includes a vector draw program that does WAY more than iDraw. It is very easy to learn & use, infinitely customizable, reasonably stable on OS 10.8, and it's absolutely free because it open-source. It has many advanced features, like envelope-warping, auto-trace, 3D & animations, none of which iDraw does.
I'm a veteran FreeHand user, (the legendary professional vector drawing program that put Illustrator to shame - which is why Adobe bought it & killed it). And I can recommend NeoDraw to anyone looking for a serious vector draw program. While NeoDraw doesn't come close to being FreeHand, it will do until something better comes along. And you can't beat the price..
Meanwhile, I'd recommend ArtBoard to anyone looking for a fun, simple, easy to use drawing app.