Can't speak to dual external monitors specifically connect to the dock specifically (as I am now down to a single 24 inch HP 1920x1200 and gave the remaining 20.1 inch 1600x1200 to my wife after it's twin died sad to say), but I have had good luck with Ubuntu 11.10 64 bit, a Thinkpad Mini Dock plus series 3 for mobile workstations and both a T410, T420 and my work W520 using one of the two display ports on the dock. I have my Thinkpad configured to disable the internal display when on AC and the lid is closed, and I typically only use the external monitor when in the dock.
However, both of my laptops have had Intel integrated graphics and, from the links, you have an nVidia card in yours. Since the bug reports are for the nouveau open source driver, have you tried to install the nVidia closed source driver in Ubuntu?
The nVidia closed source driver worked fine for me on the desktop in my sig, it has an nVidia Quadro NVS 285 low profile dual head pci express card in it and I used it for years with the dual displays mentioned above...
1) Yes, I have nVidia graphics
2) I konfirmed that KDE doesn't have this problem (installed latest Fedora x64 with KDE). However, TrueCrypt doesn't seem to work under KDE.
3) I tried installing nVidia driver but it requires Nouveau driver to be disabled. I wasted enough time trying to do this but didn't succeed. One can hate Microsoft all they want but Windows 7 x64 works on my T61 just fine out of the box.