I just experienced the exact same bug that joyrider had (see higher or click the link).
My ksoftirqd/0 was using ~20% of my CPU. Found this page via google, unloaded the cx88 modules (that i'm using for my TV Card), and ksoftirqd is now back to normal, using.. ~0.0% CPU. ;)
I'm under Ubuntu 7.10
Pentium 3 866
TV Card: Leadtek Winfast TV2000XP Expert
Haven't touched the grub config since my ubuntu install so the "nohz" option is at the default, whatever the default is.