All this stuff is now out of my engine bay! And today I filled up for the first time since I installed the MPGuino and removed the PS and AC. 36.6 mpg! This is my best tank in about 9 months, and the AC and PS were still in the car for the first 40% of the tank. I averaged over 40mpg for a 60 mile trip to the coast (with the top down and extreme performance summer tires on), and I've had some short in town trips in the upper 30's too since deleting the accessories.
Having the MPGuino there constantly reminding me to hypermile and giving me feedback on what I'm doing is immensely helpful. My mileage improvemnet without the AC and PS was immediately noticeable too.
I've been thinking about making an undertray quite a lot lately, but my car is already so low it scrapes if I don't pull into my driveway just right. I might have to wait until I move, or raise my car a bit.