Where is the netbook edition?

It's merged into the Desktop edition.

From wikipedia:

Beginning with version 10.10, Ubuntu Netbook Edition uses the Unity desktop as its desktop interface. The classic netbook interface was available in Ubuntu's software repositories as an option.

Because Ubuntu's desktop edition has moved to the same Unity interface as the netbook edition, starting with Ubuntu 11.04 the netbook edition has been merged into the desktop edition.

Here is a post from canonical blog which explains more:

Ubuntu Netbook Edition folded into Ubuntu for next release

One of the benefits of the direction that’s been taken with the next release of Ubuntu is that there is no longer a need for a separate netbook edition. The introduction of the new shell for Ubuntu means that we have a user interface that works equally well whatever the form factor of the PC. And the underlying technology works on a range of architectures including those common in netbook, notebooks, desktops or whatever you choose to run it on. Hence the need for a separate version for netbooks is removed...

So, there won't be an Ubuntu Netbook edition for future cycles - if you want to install Ubuntu on your Netbook, the normal desktop install will work just fine.

There is no netbook version of Natty, just use the regular version, they have been combined into one.

Yes, it merged with the desktop version.

No there is no separate editions to download, Both netbook and desktop versions are included in the Ubuntu.iso . this link will explain it briefly.

Since Unity there is no seperate Netbook Edition, Ubuntu and Ubuntu Netbook are the same thing now.