Does an Air Intake cause an increase in fuel consumption?

No. It might give you better fuel economy.

NO, it won't increase your fuel consumption, any increase in horsepower that isn't from an increase in fuel theoretically will give you better fuel conservation because your using other means to create power. I stress the word THEORETICALLY.

You should always check and optimize your air/fuel ratio.

I would imagine that any loss in fuel economy after getting an intake is due to the driver enjoying his new toy ;) However, I can testify that I got 40mpg w/ my short ram intake (really a dirty K&N cone filter and an adapter) when I was driving to Florida this past summer, averaging 78mph w/ an auto. I also usually get an average of 27mpg around town w/ my intake. This is in a nearly 10 year old car w/ an auto tranny.

I've definitely noticed an improvement in gas mileage with my AEM intake. I'll get some specific numbers up soon.