This is one of the best disentanglement puzzles to show up in recent years. The solution is not easy to come by. It can be assembled in a right-handed or left-handed orientation. Someone who has solved the puzzle and thinks they can take them apart easily can be really surprised if they are given one assembled the opposite of what they are used to.
It is also possible to introduce a third "W". I'm not sure to what degree, if any, it makes the puzzle more difficult.
A version is also available from Binary Arts.