Yeah, it can definitely be confusing. Interestingly, in your example, it's the location of the verb "show" that makes the difference. The non-tech user's "show me fast cars AND show me red cars" could be two separate queries appended together, which is logically similar to a single query of "show me red cars or fast cars." But that doesn't make it any easier to design a UI or to get users to do their google search properly. :)
Yeah, it is almost a verb and implied parentheses grouping there.
There's an asymmetry here, with "computer or" mapping to "human and", as my example, "computer and" kind of also mapping to "human and" ("show me cars that are fast *and* red!"), but the "human or" doesn't map to anything in a usual query.... a human reading of "show me red cars or fast cars" might be pick one of the two set of cars to show me, I don't care which.
I read an interesting paper recently about an alternative notation for boolean logic that makes it really clear what's going on. It's pretty cool!
http://alarmingdevelopment.org/?p=64
I test drove the Fit and wasn't impressed (especially after driving the Toyota Yaris & Corolla). The big problem was the jackrabbit starting acceleration followed by glacial hill & highway acceleration.