I am Ubuntu Core Developer, member of Ubuntu Installer team and have commit access to lp:wubi.
The status of Wubi is complicated =)
It has shipped on the CD and is still shipped. Primary function is to be a "cd autolauncher" for people who pop the cd into a Windows machine, at that time it says "You need to reboot, to try ubuntu! [reboot now]" or some such.
If one copies the wubi.exe off the cd, it will launch and offer Wubi based installation.
If one downloads wubi.exe off official release mirrors or releases.ubuntu.com, it also works.
It works O.K. for all defined flavours i386/amd64 builds in BIOS mode.
There is no confirmation if it works with UEFI, UEFI Windows 8, UEFI Windows 8 + SecureBoot. The last one believed to be the typical configurations of new computers that do not come with ubuntu pre-installed.
Since it's no longer an optimal solution for the default new installs, it has been de-emphasised on the ubuntu.com/download website.
Also at the moment, none of the Wubi developers have Windows8+SecureBoot or great desire to get it to code for it. If somebody steps up to write following patches:
- code to deactivate UEFI fastboot and hybrid-suspend in Windows 8
- code to integrate with Windows 8 UEFI boot-loader to offer a choice of booting Wubi and/or integrating grub2-efi+shim to boot on UEFI machines and UEFI+SecureBoot machines
Then wubi would be suitable to be promoted on ubuntu.com/download once again.
Officially it is still supported - precise has 3 more years of support, and wubi has not yet been removed from any isos and is present to download for all releases and is present on all released .isos. (12.10, 13.04, 13.10 and 12.04.x point releases)