To elaborate a bit on Paul H's post:

"A lighter bike will be quicker to get up to top speed ..."
"... a heavier bike will take longer to get up to top speed ..."

All else being equal, this is true. The amount of energy required to accelerate a mass is proportional to the mass. More mass = less acceleration for the same energy input.

"A lighter bike ... will take more energy to stay at top speed ..."
"... a heavier bike ... will use less energy to stay at top speed ..."

All else being equal, this is false. Once a mass has reached a certain velocity, the energy required to keep it at that velocity veries with the total resistance it faces. If the heavier bike and the lighter bike have the same aerodynamic drag and rolling resistance, it will take the same amount of energy to keep them at the same speed, once there. However, usually, the heavier bike has worse aerodynamics and more rolling resistance, so it will usually take more effort to maintain the same speed.

In a rolling hill scenario, you might percieve the heavier bike as taking less erengy to maintain speed, because you're carrying more momentum into the beginning of the hill.

"...a heavier bike ... can reach a higher top speed [slowly] ..."

All else being equal, the same top speed will require the same energy. However, as noted earlier, the heavier bike generally will have a lower top speed (for the same energy input) because of increased rolling resistenace and decreased aerodynamics.

"... a heavier bike ... can coast longer."

As long as the aerodynamics and rolling resistance doesn't overcome the advantage the heavier bike has in terms of momentum.

I commute on a brazed-and-lugged steel frame bike that all-in (including change of clothes for work) weighs about 32 lbs. Believe me, I'm a h@ll of a lot faster, and have more fun on my 17lb aluminum bike.

But, speed isn't everything, and I'd probably absolutely hate my commute if I took the lighter bike. The roads are crappy on my commute, and when the road is rough, steel is real (forgiving).