I think Niky gave the best commentary regarding the "Diesel vs. Gasoline/Petrol" debate. The best post I've seen because it is non-biased giving the positives and negatives of both sides.

Now it's time for me to give my non-biased viewpoint as well.

Dito kasi sa Pinas, Diesel is cheaper obviously compared to Unleaded and this is why the fuel is popular. Same goes in Europe kaya the continent is on a "Diesel Blitz". Pero in the US naman, Ultra-Low sulfur diesel is still 1-2$ more expensive than unleaded fuels and only a few stations carry biodiesel at 5-10% blend. Kaya diesel penetration for passenger cars may take a while over there.

Pero when you go to Hong Kong or Singapore or South Africa, bawal ang Diesel Passenger Cars doon (only for commercial/industrial vehicles). Kaya if you plan to drive there, don't bother looking for diesel automobiles.

So when you go those countries, you don't pick diesel but instead:
Maghanap ka nalang ng Volkswagen Golf na may 2.0 TFSI na makina.

Now onto the topic of engines.
>Diesel will always have more torque than their gas/petrol counterparts at same displacement. <-----undeniable fact
The 3.0 Diesel engine ng Veracruz still has more torque than its 3.8 V6 Lambda engine cousin (for the US market) despite the latter's 800cc advantage.
>Some diesels have same or more horsepower than gas/petrol counterparts
When you compare the Honda N22A1 engine versus the Honda-built R18A, both have same horsepower * 140hp. That's an improvement
Sa BMW, their 2.0 diesel has slightly more horsepower than its own 2.0 unleaded engine. At sa Toyota naman, where a 2.2 liter D-4D engine (2AD-FTV ; 2AD-FHV) has 7 extra hp compared to a 2.4 VVTI unit (2AZ-FE).
>Diesels have generally better fuel efficiency compared to ordinary gas/petrol engines.
No explanation needed there.

Now how about for maintenance.
>I'd say there the same.
-Diesel has more frequent repair intervals but has lesser complex components (such as spark plugs, injectors)
-Gas/petrol has longer repair intervals and is cheaper to maintain but the electronics can be a hassle if all of them are busted.

However, current diesels still have their downsides (based from what I've reasearch in the past up to now):
-Redlining is lower....or revving is at a low range.
It's no wonder pa pala na yung mga tachometer (rev meters) ng mga diesel vehicles are only up to 6000 rpm max. kumpara sa gasoline/petrol vehicles that have 8000 max rpm (with higher-performance models at 10k rpm max.)
-Thus, power tends to slow down on the higher-end of the rev range.
Diesel tends excel at the low and middle end but past there, it tends to be moot. Yet the opposite applies for gasoline/petrol engines as they tend to show their true colors when they are in the middle to the higher end of the powerband.
Best example is the 3.7 engine ng Nissan group. The VQ37VHR really "tempts" the driver to push it past 6-7.5k rpm and beyond.

Dashboard of Infiniti G37/Nissan Skyline 370GT


Probably explains why Porsche doesn't make diesel engines atm.

>Gasoline/petrol still have the edge in straight-line acceleration.
Even up to now till the end of this decade, I think this will still remain true. We will see though if something surprising happens from the diesel camp come by post-2010.
>Manufacturers still improving their own gasoline/petrol engines
Despite improvements in diesel, the car makers are also improving on their unleaded engines at the same time. Most especially sa mga euro car brands where diesel is king for them, they are still improving engines using the other fuel (ie. VAG with their TFSI engine, MB with their CGI Twinspark, Volvo/Ford with their 3.2 V6 and T6 engines and so forth).

So there. A sum-up of potential pros and cons from both fuel technologies.

I'd say that atm, they are pretty evenly-matched (I agree with niky's viewpoint) IMHO. Although things can change by the next decade though so we should see how this battle heats up (lalo na when Nissan releases its next-gen 3.0 V6 by 2010 with up to 30 km/liter of FC)

What you do want to see though for the next decade are:
DIESEL HYBRIDS (best of both worlds).

Once these things launch, magkakaroon na ng competition para magkaroon ng drastic improvements to gasoline/petrol hybrids (which would push for 100+ km/liter due to competition from diesel hybrids )

Then after 2020, we will start to see the dawn of the hydrogen and electric-powered vehicles

Just make sure nga lang na buhay pa kayo by that time so that you can witness some really sophisticated engine technology.