What is Dry Sump?

While looking at a few bikes on my quest for a new machine...i have noticed a few have Dry Sumps.... Yamahas, Suzuki DRZ etc.

What is the benefit or downfall of this?

Does it help the longevity of the motor?
Why do they do it?

Wet sump means that the engine oil sits in the bottom of the engine. This is typical in american cars, lawnmower engines, etc. The sump has to be deep enough so that the crank does not hit the oil in the bottom. If it does it saps power, adds heat, and worst of all can whip the oil into an oil and air froth that does not lubricate very well.

In a dry sump engine, there is an extra oil pump that sucks oil out of the engine sump and pumps it into a seperate tank.

Advantges are:
-engine can be a little shorter
-seperate tank can shed more heat
-on motorcycles, the frame can act as the oil tank which saves having to have a tank
-if the tank is a seperate tank, you can make it tall and thin which helps get the air out.

Disadvantages:
-extra stuff on the bike (oil lines, tank) costs more and, well, is extra. More stuff to deal with when you pull the engine, and slightly more weight.
-if you blow the motor up and the frame is the oil tank, you may have a difficult job of cleaning it out.

Lower (shorter) engine and better cooling.

Dry hump is when a guy and girl rub up against each other with their clothes on.

A Dry sump engine uses two oil pumps, one to feed oil to the engine bearings, and another pump to "scavenge" the oil from the bottom of the crankcase, and return it to the oil tank. There are several reasons for doing this, one is to reduce loading on the crankshaft. If the crank shaft runs in a bath of oil, horsepower is lost, other reasons for getting the oil out of the sump are foaming and cooling. There's no disadvantages to dry sup engine designs, other than adding additional cost and weight to a bike.