My experience with Windows installer -
it doesn't ask you about partitions,
it crashes everything, creates the partitions by itself and extracts the system.
Selection/creation of partitions is a barrier. One more barrier which makes N% of interested people cancel (delay to N years) the installation of eCS.
Do people install several OSes to one hard drive?
Usually they install 1 OS to 1 partition.
This related to eCS too.
IMHO, eCS installer should offer:
1) "Empty hard drive and install eCS to 1 parition"
2) "Edit partitions (eCS installer has this dialogs already), Select partition for installation.
Of course, if 1) is selected, the installer should prepare partitions and start installation without reboot.