tried it. i like it. it's a fun little app. i don't know how much i'll be using it but i'm glad it's savable. one thing i noticed though was a bit of delay with the rendering of the path where my finger runs through. i'm using a motorola droid and i know it can handle faster response with the rendering of the "paint" after my finger. not sure if there's anything you can do about that.
I'll admit I haven't tried your app yet on my Eris, but will try to do so tonight. My kids, 7 & 4, love the "fingerpainting" and drawing apps, and I'm sure others' children do too. Keep that audience in mind as well as the adult audience.
You've got the right idea coming on here to get feedback on your app. Good luck with it!
Sone, I downloaded it and played with it a bit. It's nice and fairly easy to use, but to be honest, I don't see anything that much separates it from the field other than the shape feature and the blur or anti-alias option. At some point it seems that drawing is just drawing. As I mentioned before, my kids love Magic Marker (which lets them draw with kind of a neon glow) and FingerPaint. I don't know that there's anything here that would dramatically differentiate Graffi from these.
One thing I haven't seen in any of these is a "coloring book" type template -- where you link to some outline drawings that could be colored with the Graffi program. That might be something that kids and adults both could enjoy and could separate your program from the pack. Not sure how you would accomplish that, but I've not seen that in other programs. Most will allow you to draw on existing pics/photos, but haven't seen any that provide stock outline or "coloring book" templates.
I don't mean to be negative, but hopefully this is constructive for you.