I am currently running Windows 8 Release Preview build on my R400 (nearly identical to T400). I have to say that it runs very well on the C2D P8400. I have successfully installed Access Connections, Power Manager, Lenovo Device Experience, tpfancontrol, and UltraNav.
The things that don't work include ThinkPad System Update, ThinkPad Toolbox (PC Doctor), the blue ThinkVantage button, and the MUTE button. All of the drivers had to be downloaded individually from the lenovo support site. Install time and boot up time is extremely fast, even on a traditional spinning hard drive. I have Windows 8 on a separate partition and Dual booting with Windows 7 works very well.
R400 7439W1K- 8GB, Momentus XT 500GB, Intel 5300 WiFi
T410 2518X01- 8GB, Corsair Force GT 120GB
T410s 2901A3U- 8GB, Intel 6300 WiFi
T420s 4174PPU- 16GB, Intel 520-series 7mm 180GB & Crucial m4 mSATA 256GB, Intel 6300 WiFi
and a few classics in storage