Hm. Thanks for the heads up. I just fixed that link. It now points to an HTML version of the paper.

As to difficulty, it can be cracked in hours. In certain circumstances, it can be cracked in minutes. Horsepower isn't necessary. What's needed is a good sampling of the traffic, including the initialization vectors (IVs).

This is difficult to get in a mobile scenario, unless you're on a busy network (e.g., a company network). In a home scenario, the frequency of computers establishing a session with the AP will be low, and it will take much longer to collect the necessary data. This is bad for people trying to hack WEP by strolling or driving by, but of no consequence to neighbors, who have as much time as necessary to collect the data.

So, it's not like you need to go build Deep Crack ($10,000 homebrew kit for breaking DES in real time), but it's not as simple as ROT13ing the data stream, either.