Upgraded the Thinkpad T21 to kernel 2.6. Fairly painless, and things look like they are moving more quickly.
Major annoyance is the T21’s built-in 3Com mini-PCI ethernet/modem. It seems to hate all the power-management goodies that ACPI gives, and will only work under the older APM. It seems the solution is replacing the 3Com board with the Intel PRO/100 SP mini-PCI board, and all may be well.