There’s a problem with the iwlagn wireless driver that ships with Jaunty by default, and you’ll find that when wireless connectivity drops you’ll have errors like these in your dmesg log:
[126774.231915] iwlagn: Microcode SW error detected. Restarting 0x2000000.
[126774.252811] iwlagn: MAC is in deep sleep!
Now, you can reset the connection easily enough with sudo ifdown wlan0 && sudo ifup wlan0, but thankfully the fix is already in the updated version of the iwglan driver in backports, so just go:
sudo apt-get install linux-backports-modules-jaunty
A swift reboot later and wireless ain’t gonna drop out on you any time soon – hurrah!