Upgrading a sparc64 SMP box from 2.4.32 (solid but doesn't have a number of features the newer libc needs) to 18.104.22.168 has taken me since 18:00, Wednesday.
2.6 on UltraSparcs is...painful. The iptables recent module kernel oopses immediately on load, some other iptables mods are simply not available and still others have been buggy for years, the md subsystem doesn't properly deal with the older meta info, the LVM subsystem definitely fucks up the older lvm metainfo badly (in the end I had to nix one vg hard, via dd across its pvs, and restore it from backup), booting into a ripped-apart mirror doesn't work anymore unless lots of extra kernel params are given etc. etc.
fuck Fuck FUCK! damn all-the-world's-an-intel weenies.