Well, I drive a diesel Mercedes Benz 300D every day and I love it. With the higher fuel economy and lower maintenance costs, it would take a lot to get me back into a gas powered car.
Diesel engines get better fuel economy simply because they do not need to burn as much fuel as a gas engine to get the same power. Diesel engines are also built heavier than a gas engine to sustain the added stress of the higher compression ratio. Diesel engines do not have an ignition system so you will never have to tune them up. Exhaust systems last longer because diesel fuel exhaust is not as corrosive a gasoline engine exhaust.
It is not unusual to see a diesel engine with 400,000, 500,000 and I have even seen them go as much as 600,000 miles.
The down side is they are fairly noisy. You will get the typical diesel clatter at idle, but that goes away off idle. At normal driving speeds they are as quiet as a gasoline engine. You won't get the same acceleration that you get from a gasoline engine. But a turbo diesel will get up and go fairly quickly. You will need to adjust your driving habits somewhat also.
As for maintenance, 3,000 mile oil changes are a must! Diesel fuel is not as refined as gasoline and the oil will get dirtier than a gasoline engine. I recommend replacing air and fuel filters once a year. If you live in a cold climate, you will need to switch to a winter blend fuel to prevent fuel gelling. There are additives you can put in the fuel to help prevent this as well.
I also recommend replacing glow plugs every two years as well. If temperatures drop below 10 degrees F, I would also recommend a block heater. This will insure cold weather starts, especially with the heavier grade oil that diesel engines require.