Even the most efficient internal combustion engine is only coming in at about 35%, so the difference is rather negligible, wouldn’t you say?
Not to mention the added benefit that we’d probably re-charge our vehicles on our employers’ dime whenever possible. 
Hybrids really are not that useful in actually reducing harmful emissions, but they make a great political statement. New conventional gas burning cars such as the Honda Fit and Toyota Yaris are greatly improving fuel economy. I think the only mistake with these lines is they are being marketed as stripped-down low-budget vehicles. Most of you should remember how well the Yugo went over a few years ago. But at least public consciousness is raised and manufacturers’ seem to be taking notice. However, I’m sure it’s not lost on them either that 2007 Yukon’s and Tahoe’s are selling like hotcakes as well… sigh
What would really help would be if folks would slow down, keep their tires properly inflated, reduce trips, and carpool as often as possible. But that requires a lot more personal sacrifice and isn’t anywhere near as sexy as a new Prius.
While that sentiment is often expressed, in fact it would help very little to reduce world petroleum consumption. How do we know for sure? Simple:
Consider a more extreme hypothetical fuel conservation measure. Assume that EVERY 2-car US household sells one vehicle and buys a Toyota Prius. 100% compliance. Every 2-car household. What difference would this make?
Background info:
US gasoline consumption is roughly 44% of total US oil consumption, or
9 billion barrels/day. Total consumption is about 20 billion barrels/day.
US fleet economy average (2004): approx. 21 mpg
Prius actual gas mileage (Consumer Reports): Roughly 44 mpg:
http://autos.msn.com/advice/CRArt.aspx?contentid=4023458
Approx 100 million US households
About 25% drive no vehicle
About 25% are 2 (or more) vehicle households
About 50% are 1 vehicle households
So 25% of vehicles would roughly double their mileage from 21 to 44 mpg.
The average mpg increase of the total US fleet would be from about 21 mpg to 28 mpg, roughly a 33% increase in mpg.
Thus the 44% of US oil consumption would decrease by 33%, thus causing total daily US oil consumption to decrease from 20 billion barrels/day to 17 billion barrels/day, or a 15% total decrease in US oil consumption.
Now 15% decrease is superb, but since annual energy consumption increases at about 2-3% per year (it’s scaled roughly to economic output), that drastic step bought you 5-7 years. After that you’ll be right back where you started in terms
of energy consumption. Plus during that 5-7 year period you’re STILL consuming petroleum at fantastic rates, just a little less than before.
It would temporarily reduce oil prices quite a bit, from decreased demand. There could be geopolitical advantages. However it would effectively make no difference in time to peak oil, which is the big problem.
If every single US two-car household getting a Prius makes little long-term difference in the big picture, other smaller measures such as inflating your tires and increased mass transit would be miniscule.
Consider western Europe for comparison, which uses much more mass transit, more centralized development and smaller, more efficient cars. Yet western Europe’s energy consumption per GDP dollar is about equal to the US:
http://www.dallasfed.org/news/educate/2004/04ecsummit-brown.pdf
That’s not to say properly inflating your tires is a bad idea. It reduces tire wear, increases safety, improves gas mileage a little, and costs nothing. In that sense it’s worth doing. But that along with all the other mentioned steps will not solve the petroleum situation. The problem isn’t that people are too selfish to take those steps, rather those steps even if taken would be insufficient.
You make excellent points, but don’t underestimate the energy savings I mentioned:
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Reducing Speed: Here’s a real world example demonstrating a 40% increase in fuel economy by driving 55mph instead of 70mph. A smaller, but still significant benefit was achieved in a more scientific study using a Civic hybrid.
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Proper tire inflation: We can thank dear Cecil for his report on this subject. In short, expect a 5-20% increase in fuel economy if you check your tire pressure once a month.
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This cannot be adequately estimated using scientific methods. But simply put if you can walk to your destination, you’ll reduce your petroleum consumption approximately 100% or more. (Factoring in the difference in tread wear between your tires and the soles of your shoes, less any maize-based food you may have consumed) Plus the added benefits of combating obesity, and its associated health problems. Likewise, combining multiple errands into a single well-planned trip can save huge amounts over driving to each stop individually and returning home after each trip.
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This is as subjective as #3, though assuming you carpooled daily with one other commuter, you’d reduce your fuel consumption associated with your commute by nearly 50% (Less lost fuel efficiency due to the weight of the additional passenger plus any additional distance traveled in picking up your passenger)
Making a serious commitment to each of my four suggestions though can easily increase your overall MPG far more than simply replacing your average late model vehicle with a hybrid yet maintaining your existing driving habits.