First, there was the announcement of the:
Ubuntu Mobile and Embedded Edition
This was an extension of the GNOME Mobile and Embedded Initiative however it was confusing to many people mainly because of the preexisting Ubuntu Embedded Team which was working to get something like emdebian working for Ubuntu. The Ubuntu Embedded team was mainly looking at getting Ubuntu working on ARM based devices
The Ubuntu Mobile and Embedded Team starts work and as time passed, most of the focus was on getting hildon and moblin into Ubuntu, and porting to the new lpia architecture from Intel.
During the hardy cycle, there was work towards getting something to work on various devices, based on the "menlow" and "mccaslin" platforms from Intel.This work didn't complete within the hardy cycle, and continued in a PPA.
This resulted in the first release image of Ubuntu MID.
Ubuntu Mobile Team
Due to nomenclature cleanups, the Ubuntu Mobile and Embedded Team became the Ubuntu Mobile Team, as the goals were increasingly divergent from those of the Ubuntu Embedded Team.
So in summary:
Sometime after hardy, Ubuntu MID was first released from a PPA, and was the work of the team now known as the Ubuntu Mobile Team. While this release was always targeted for 4-6" screen devices most of the testing and the work was done on the Samsung Q1 or on somewhat awkward development kits.
Netbook Remix
Completely independently, a set of Canonical developers from the OEM team was looking at technologies to support the new "netbook" devices.
Using a mix of GNOME, Open Hand stuff, some of the work that went into Ubuntu MID, and additional development, they produced the "Netbook Remix", based loosely on Ubuntu Hardy. This Remix included 4 new packages, and patches to about 59 more.
The resulting Netbook Remix was released previously to the first release of Ubuntu MID. A very good summary of the reasoning and ideas behind the Netbook Remix can be found here
UDS Intrepid
At the UDS for intrepid, there were demonstrations of preliminary versions of both the Netbook Remix and Ubuntu MID. There were also demonstrations of additional stuff based on Ubuntu MID done by the Canonical OEM team. Along with this were further demonstrations done of the Edubuntu CMPC image.
As a result of all this it was determined that there should be an Ubuntu Mobile flavour.
Intrepid
So, for Intrepid, there is work to create Ubuntu Mobile. This is designed for 7-9" screens, and is likely to work best on the Samsung Q1 (as that happens to be the 7-9" hardware most likely to be owned by the developers working on this flavour).
Ubuntu Mobile doesn't have any of the hardware settings or hardcoded configuration that was present in the Hardy-based Ubuntu MID, and so should not be nearly so tied to the specific device.
Additionally, one of the goals for Intrepid for Ubuntu MID was to move away from all the hardcoding, and so enable a wider variety of devices (perhaps including appropriately sized hardware like the Aigo MID or Sharp D4).
Intrepid will have an ubuntu-mid.img as well as a ubuntu-mobile.img While the latter is only a snapshot release to base further work in jaunty on, the mid image will actually be an improved one from the original hardy release
Jaunty
Will likely be based on hildon 2.2 which is itself supposed to be based on clutter/gtk. This will likely bring significant improvements for Ubuntu Mobile.