What makes the semantic web such a difficult thing to implement in a useful way is, again, a combination of the limitations in the technology, but most of all the human factor. It just isnt possible to model human behavior. There is mood, taste, circumstances, irrational behavior and all other types of complexities that we humans can deal with (barely) but machines cant.
I think the semantic web has a long way to go. Anyone remember virtual reality video games. Sometimes the concept is great, but it will take time for it to be accessible enough for the average person to understand, let alone adopt.