Say what you like about the Prius (as Zulu77 alludes to, both the driving experience and the looks are probably a "love or hate" thing) but it does return the fuel economy - in the right scenario.
I had an extended taxi ride across Milan in rush hour in a Prius a year or so back.
We are talking the stereotypical Italian taxi driver. Boolean throttle and brake controls, taking off from every set of lights flat out despite that fact that the next set of lights 300 yds up the road are clearly just turning red, etc. etc.
When I got into the car I saw the average fuel consumption figure (in l/100km, of course) and it seemed infeasibly low. Spent the first half of the journey doing mental arithmetic and working out that we were talking high 50's verging on 60MPG.

Once I'd worked that out, I remember sniggering before taking a second look at the average, thinking that this traffic and driving style would have done it no good. It had actually improved.

I doubt any conventional petrol car would have bettered 30 MPG on that run. An Omega, although a bigger car, would have been doing about 15MPG without a doubt.
Comparing it to a conventional car on the motorway is pointless. They are both propelling themselves exclusively by petrol engine. Both engines are operating in a reasonably efficient regime but the Prius is hobbled by a bootload of batteries and electric motors.
Where hybrids really come into their own is in city traffic where they avoid operating the petrol engine in its most hideously inefficient mode.
I don't do any city driving but if I did have to on a daily basis, I think they'd be more worthy of my consideration. The only thing that would worry me is long term maintenance costs, bearing in mind I tend to buy cars once depreciation has made them better value for money. No battery technology has yet produced batteries that last terribly long and replacing a Hybrid's batteries must be eye-wateringly expensive.
Kevin