So here's the situation: I'm in an area with several competing WiFi hotspots. For some reason, no matter how many times I kept manually entering the ESSID on the Network configuration dialog, I just could not hook up to any of the access points. Had something gone wrong with my network configuration, I wondered?
I stumbled on the solution by accident as I plugged in an Xubuntu LiveCD. (No, this solution does not require you to burn and boot from any LiveCD. It was just the means by which I figured out the solution.)
So anyway, here's the trick:
Leave the WiFi interface of your computer unchecked. That's right. Don't enable it. As you enter the WiFi zone, you'll note that the WiFi indicator should light up.
Open up a terminal and activate the interface. You do this by entering
sudo ifup eth0(just replace eth0 with your proper WiFi network device.)
After that, your WiFi should work properly.
I know it's strange. I don't know why this kludge works, but it does.