I have a Viewsonic G-Tablet that I've been experimenting with for a while. The problem with running pure Linux is the lack of drivers. Video drivers for Tegra 2, wifi drivers and drivers that are used to access the webcam.
XDA-Developers and SlateDroid have threads that talk about installing Linux inside Android, but that's not the same as running pure Linux.
Droid Basement has kernels that are developed for mobile devices including tablets, here's the link:
I bought the G-Tablet because I thought Nvidia would keep updating the drivers, but, after Froyo, the older devices were abandoned and newer drivers were built for newer devices/components. Which means, unless someone can engineer new drivers to work with newer kernels, we're all stuck with a non-updatable tablet. There are many who are trying, but, a stable honeycomb or ICS for older Froyo built tablets has been illusive. They come close, but, everytime there's a problem, it's usually caused by the lack of a newer driver or workable module.
You might also be interested in this http://developer.nvidia.com/linux-tegra . While this doesn't really cover the harmony platform that my G-Tablet was built on, newer tablets that use the Cardhu or Ventana platforms might be able to use it to build a pure Linux tablet.
By the way good luck, and, keep us informed with what you come up with.
BTW - Searching through the Slatedroid and XDA-Developer sites and reading up on what problems the devs are working on will help you get a good start. No need to duplicate the work they've already done.
Hope this helps.