Today, just for giggles I grabbed a spare USB Linksys WiFi b/g adapter off my desk and plugged it into my EEE PC. It was imediately recognized and available for use which I wasn't really expecting. Generally in Ubuntu to have to go through driver hell to make one of these work.
But then ... I couldn't actually join any networks that I found and I really didn't care to. What I was interested in seeing was what the signal strength looked like in comparison with the internal Atheros card. This was easily viualized simply by showing the list of available networks. As you can see by the screenshot here, the external USB was about 20+ percent more powerful.