The latest issue of MAKE (Issue 16 on "Spy Tech") has an article I wrote that shows how to hack a Glade "Wisp" and drive it from an Arduino. Yeah, it's a weird idea, but it has some interesting uses (DIY Smell-O-Vision, just to mention one.)
Glade Wisp: http://www.amazon.com/S-C-Johnson-22628-Fragrancer/dp/B000ASBFVA
The Wisp use a piezoelectric disc to atomize aromatic oils and I show how you can hack the drive circuit and spray out puff of scent on command using only a few lines of Arduino code. And, for more fun, you can easily replace the prepackaged scents with your own.
My daughter and I are building a dog training device based on scents, but I can imagine a few art projects that might find a use for this idea, too. Anyway, it was a fun hack to do and I hope someone else finds a use for it, as well.
Wayne