I'm as much a LMCE noob as anyone here, but from what I've seen of the scripts, it is highly unlikely that an uninstallation is possible. I have a few suggestions for the Powers That Be that relate to this, which I'll get to in a moment.
The way the installer is built, it basically takes over the system, making it impossible (or at least undesirable) to have LinuxMCE installed on a regular workstation. It just breaks too many things, aside from the fact that it breaks LinuxMCE in itself (I've been trying to get this working for several hours, with no luck, and I'm no Linux or Ubuntu noob).
So how about two additional methods of distribution?
1) Make a LinuxMCE LiveCD. You won't have to bother with an installer (or uninstaller), since everything will just be pre-installed on the CD. I don't know how challenging that would be to make, but it would sure be easier on the end-users, especially your target audience which is not necessarity techno-savvy who just wants to see live those wonderful features shown on the video.
2) Every single piece of good software I know of has first been adopted by geeks, and the geeks then sell it to the "normal people". So why not document and distribute the tools to an entirely manual installation, where the user can have control over when and how they will break their system? As it is, the current installer breaks MANY things on an otherwise unchanged Ubuntu 6.10 desktop install.
Don't get me wrong, I still think LinuxMCE is going to be one of the more important open-source projects, right up there with Asterisk and MythTV. But the fact remains that in my experience it was easier to install MythTV from source (and with a good Howto) than LinuxMCE with a fully automated (and broken) installer.
At the very least, at this point in development I think it should be advertised in bold red letters that one should NOT try to install LinuxMCE on one's everyday-use Ubuntu 6.10 workstation or desktop, as it is not at all a set of well-behaved packages.
And now, I'm off to format my HD and reinstall Ubuntu...