I purchased a Raspberry Pi a few weeks back. I found that I could power it, a WiFi card and a GPS from my 12000mah Li-Ion battery pack for about 12 hours. What a great way to explore with out having to have a huge laptop or giant battery in my bag.
From that I did a little bit of driving and biking with this tool kit, passively looking for and logging networks. I could have easily used my NinjaTel phone (and will attempt this in the future), but I wanted something that I didn’t have to mess with to much and would have a long batter life to “power all the things”.
From this I found that out of 6,164 APs identified, that only %5 had WEP configured (which is flawed). That is a total of 327 APs that still had WEP enabled. Not to bad as a basic health check. Of course more data would always be better.