Wubi allows for Ubuntu Linux to be installed on a Microsoft Windows host that you can then launch at boot-time but without having to re-partition the drive, etc. It's a nice concept, but the Ubuntu Wubi performance is slow for I/O access.
Earlier this year it looked like Wubi might be dropped, but now it seems developers instead will try to redesign the Windows installer for Ubuntu 13.04.
Plans that were discussed yesterday at UDS-R Copenhagen for Wubi include support for burning to a USB stick, integrated CD burning of Ubuntu, a visual refresh to the user-interface, and better uninstall support. There's also a "wish list item" of having Wubi be able to handle a full-disk encrypted Windows installation.