I've been thinking about this for a while, and instead of putting down the money for a kit with pump, injector, and controller, I was just thinking of doing this:
The only thing I'm waiting for is the time to get started on all my projects.
This isn't as good as mist injection, but this more closely resembles driving on a foggy night which has shown to increase fuel economy. Plus, this setup is practically free.
I think it'll work, because unlike a lot of MPG enhancers, the science behind this idea is sound. If you try it out, be sure to let us know how it works.