WEP and MAC filtering both have their uses in the right setting. For starters, if you have a TIVO or PSP, in your house that's all you can support.... Also, as Yuri mentioned, MAC filtering has no overhead. I frequently work with my other machines and my server from my laptop and encryption is noticeable. Even for internet connections, it does introduce a latency that's not there natively. Because of the double encoding, it's noticeable in an SSH session. As for location, unless you are fairly urban, all I need to keep out are two not-so-nosey neighbors and the occasional drive by contractor. In this case, anything that requires more than a cursory knowledge/effort is fine...
If you're really wireless security conscious, install IPcop, put the wireless on the "blue" network, and VPN into your own LAN from the couch. That's what I install for all my buddies in Al Quaeda cells.
It's far cheaper/easier to send the spam off open relays. As for the war drivers, it does happen, but unless you are in a high density area it generally ranges from non-existent to benign. I do it myself when I'm out of town and need net access in a weird area. Like our last camping trip. I got a support call from work that required attention. I just drove to the nearest subdivision (about 5 miles) and leeched for about 1/2 hour till I got the problem fixed. Had that failed, I would have dialed in the GPS to the nearest McDonald's or Krystal.