My system spontaneously started thrashing again this morning and this time it did in fact turn out to be caused by amule. Although the system became unresponsive, I was finally able to shutdown X with ctrl-alt-backspace and log into a failsafe terminal. Here is the output from top which I saved to disk:
$ cat toplog.txt
top - 12:19:25 up 1 day, 11:41, 3 users, load average: 1.69, 9.37, 12.31
Tasks: 95 total, 1 running, 94 sleeping, 0 stopped, 0 zombie
Cpu(s): 20.6% us, 1.9% sy, 0.0% ni, 0.0% id, 77.5% wa, 0.0% hi, 0.0% si
Mem: 1035176k total, 1020624k used, 14552k free, 620k buffers
Swap: 1020116k total, 534784k used, 485332k free, 10812k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3049 jrb 18 0 1339m 899m 2492 D 21.1 89.0 262:51.90 amule
157 root 15 0 0 0 0 S 0.3 0.0 0:37.54 kswapd0
2347 root 15 0 0 0 0 S 0.3 0.0 0:10.13 nfsd
1 root 16 0 1992 104 80 S 0.0 0.0 0:01.22 init
2 root 34 19 0 0 0 S 0.0 0.0 0:00.48 ksoftirqd/0
3 root RT 0 0 0 0 S 0.0 0.0 0:00.00 watchdog/0
4 root 10 -5 0 0 0 S 0.0 0.0 0:00.32 events/0
5 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 khelper
6 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kthread
8 root 10 -5 0 0 0 S 0.0 0.0 0:00.62 kblockd/0
9 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 kacpid
100 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 khubd
158 root 18 -5 0 0 0 S 0.0 0.0 0:00.00 aio/0
245 root 10 -5 0 0 0 S 0.0 0.0 0:00.02 kseriod
320 root 11 -5 0 0 0 S 0.0 0.0 0:00.00 kpsmoused
336 root 10 -5 0 0 0 S 0.0 0.0 0:00.02 ata/0
340 root 11 -5 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_0
As you can see, amule was still running and using a catastrophic amount of memory, nearly 900M on a 1 GB machine. For some reason it had not responded to the Gnome logout and I could only terminate it with killall -9.
FWIW: amule had been running about 36 hours. Yes, I am sharing a lot of files.
At this point, I don't think it has anything to do with ext connections; I had that function disabled and amuleweb was not running. This is the 1 April CVS with wxGTK-2.6.2-5.fc5.
Let me know if I can supply any additional information...