Here's a philosophical thing. Depending on how often you carry a bike on the roof, if you have room inside the vehicle normally, and what kind of mileage you get, you may not want to use your roof rack a lot.

For me, in a car that gets 45-50 mpg on the highway, and room for 2-4 bikes inside, it doesn't make sense to put anything on the roof. We've taken two bikes (two people), luggage, etc, without any problems (small station wagon).

I've seen people show up at races with a roof rack, one bike on it, and an otherwise empty relatively large SUV.

The rack alone will take a few mpg off, maybe 2 or 3 for my car; putting the bikes up can take 10 mpg on my car - instead of consistent 40-70 mpg on at 70 mph, we were getting consistent 25-40 mpg (uphills and flats; downhills the mileage is much higher).

We use the rack when carrying more than 2 bikes, when we have 3-4 people in the car, or when carrying our tandem, or all of the above.

I can install and remove the rack by myself in about 10 minutes. Two of us, about 5 min. Depending on how busy I am it's worth it to me to take the rack off; we normally remove the rack as soon as we return from a long trip.

It costs me about a dollar to go 10 miles (40 mpg, avg of city and highway, $4/gal). I figure I'll be getting 38 mpg with the rack on (no bikes), so I spend an extra dollar every 190 miles. With bikes on top (and a full car) we barely broke 30 mpg. What's that unused rack on top worth to you?

Of course there's the political aspect of it too - former head of CIA James Woosley on how the US subsidizes Al Qaeda.
http://www.motortrend.com/features/1...w/viewall.html
I like his idea of "miles per Saudi gallon" instead of just straight out "mpg".