Quite honestly, it didn't work as well as I thought it would. I had grand visions of using my 3 gallon bucket of soapy water to clean the inside vinyl and then washing the outside of the car until it was a lovely, gleaming grey(yes, I recently was informed that my car is grey, not black. My recent parking ticket, the DMV and Matthew have all three insisted on this point; it was a surprise to me). Really, the dish soap that I used didn't cut through the brown grit like I expected it to and I suppose the kitchen sponge I used wasn't truly adequate for the job. Oh well, it looks slightly better than it did with it's streaky brown patches of dirt covering the hood, trunk lid and top of the car, and besides, using only 3 gallons of water for the entire car bath is far more environmentally friendly than using a car wash. Although I think giving my car a sponge bath is pretty high up on the crazy scale, I still don't think it competes with taking a rag mop to the car like a former acquaintance of mine once did.
I also discovered that my roomba is not designed for vacuuming the floors of a car. He did absolutely nothing to suck up the dirt but did successfully managed to fling the dirt and other collected filth in a little circle, away from his little body. He's cute.