i think the answer here really is, the regular chaps among us wont be cracking no WEP key, it just simply isnt that simple unless you are able to learn how to use the various software tools required (Aircrack-ng, wireshark, commview etc etc etc) and use that data to crack a key. the time it takes is also a factor, quite simply you have to be adept with the software if you want to crack someones WEp key, but most people just dont use them (although scanning my neighbours now i found one using WEP, so I had a quick look at their packets-can see they are using an iPhone lol).
The USB pen on ebay just has a ton of the software, which is all well and good-its USING that software thats the problem!
also, its illegal I believe, hacking anybodies network without their permission? so just be careful, if you try to hack, you too can be hacked!
all good fun.
p.s. no feathers ruffled here at all, its complex but interesting topic!