For the record: Ubuntu 10.04 (Lucid Lynx) is working great on the Asus Eeepc 901. Only the support for the RaLink RT2860 wireless chip is not that great, sometimes the system refuses to connect to a wireless network. The best approach seems to be installing the backport package that brings a newer version of the driver:
sudo apt-get install linux-backports-modules-wireless-lucid-generic
or when the PAE kernel is being used:
sudo apt-get install linux-backports-modules-wireless-lucid-generic-pae
Connectivity is much better for me with the updated driver.