Turn radius.
 

Another thing I have noticed is how the way you make a turn greatly influences coasting. I make a left turn at this roundabout, twice a day. I approach in the left hand lane (right hand lane is for vehicles turning right) and follow the kerb round into the steadily steepening downhill section. However, in the morning when there is no traffic about I use the right hand lane, clip the kerb and continue out towards the centre line of the road down the hill.
Approaching at exactly the same speed, the second option sees me leaving the roundabout with less loss of momentum, greater speed, and sooner able to engage 3rd gear to enjoy DFCO as I descend the hill to the next roundabout.
http://i.imgur.com/g7kc2b4.jpg
Obviously this scrubbing off of energy happens every time you take a corner though most drivers are not aware of it (and possibly many hypermilers). So by taking the largest radius you safely and legally can, through every corner, you will end up burning less fuel.
I keep learning. It amazes even me!

I've also noticed how much speed gets scrubbed off around turns. As much fun as turns are, it's more efficient to coast down to a lower speed prior to the corner. Better to coast longer than brake with the steering wheel! Of course "straightening" the corners like you do helps too.

The center of that roundabout would be great for getting up on two wheels! :D

There are a couple of bus drivers that could vouch for that!

Remember, from high school physics, that turning == acceleration.

If you make a 90 degree turn, say from west to north, all the while maintaining 30km/h, you have to accelerate from 0km/h in a northerly direction to 30km/h in a northerly direction. You can get most of the energy to do that from the deceleration (technically, acceleration from 30 to 0km/h) in the westerly direction, but since nothing is 100% efficient in the real world (especially in government work), you'll need to add some energy from the engine.

The sharper you turn, the more energy you lose due to friction (mostly in the back wheels, where the tires aren't pointing in exactly the right direction during the turn), so the more you have to add back in from the engine.

Case in point: A downhill serpentine in the Oregon Coast Range.

There is a line of minimum effort through each/every corner, it starts wide then dips down to the apex and runs wide again on exit.

If the corners are spaced regularly and alternately, the line for each succesive corner meets in the middle. So the car rolls to one side through the corner, then a flick of the steering wheel and it rolls to the other side and holds that through the next corner. Rinse and repeat.