Some X.Org developers have been looking at mobile GPU switching support, but so far, that has not amounted to anything. For now, Linux users are limited to choosing one graphics processor to use prior to booting into Linux. The Lenovo ThinkPad T400 supports choosing the graphics processor to use from the BIOS. Hopefully in the not too distant future this feature will be supported on Linux.
Beyond the switchable graphics not being switchable on Linux, the only other real area that had not worked with Ubuntu 8.10 was the integrated fingerprint reader. The ThinkPad T400 uses a fingerprint reader designed around an AuthenTec chipset and the available Linux drivers had not worked. The WiFi, Bluetooth, audio, web-cam, and ACPI features all worked with this notebook "out of the box" on Ubuntu 8.10.
When it comes to the performance of this notebook, we ran a number of different tests on it using the Phoronix Test Suite. Benchmarks comparing the performance of the Lenovo ThinkPad T400 to another Intel Centrino notebook can be found in our Dell Inspiron 1525 review. There are a number of graphics tests from the Intel IGP on the T400 in Intel Graphics Regressions in Ubuntu 9.04? Benchmarks from Ubuntu, Linux Mint, and gOS on the T400 can be found in this performance comparison. Lastly, thermal results for this notebook can be found in the NZXT Cryo LX cooler review. The only real sore point for the Lenovo ThinkPad T400 and Linux is the lack of switchable graphics support, but that hopefully will not end up being a permanent hurdle. Besides that, this notebook is compatible with Linux and does offer great performance along with the ThinkPad build quality and reputation we have come to know over the years.
Reviews and pricing information on Lenovo ThinkPads and other notebooks can be found at TestFreaks.com.