The same problem has been observed by someone else with an R61 with an Ubuntu 2.6.26 kernel. After I upgraded to 2.6.28, the problem disappeared altogether. As Lenny was released with 2.6.26, but I'm running sid and have been using sid's 2.6.28 for a while, and now a self-built 2.6.29, I can neither confirm nor deny whether Lenny's kernel is stable on a ThinkPad R61.