I've recently been getting strange system lock-ups - often my system
just dies, but occasionally I get messages in dmesg. I've tried to
isolate the problem by increasing the available swap (I now have > 2x
RAM), removing my reiserfs partitions (I'm now running with ext2) and
downgrading from kernel 2.4.5 to 2.4.4, but I'm still seeing the
problem.

Here are the two logs that I've been able to get - after I got these
logs I rebooted my machine and it failed to unmount my /home partition
with the message "device busy".

The first one happened on June 4th with a 2.4.5 kernel: