I find it far more likely that we'll have built a practical AI before the semantic web ever happens, at which point all semantic efforts will be obsolete.
Of course, if there's anything more masturbatory than the semantic web, it's microformats. Hey! You there! Don't link to a vcard object, that's yesterday's deal. Instead, painstakingly reproduce your vcard in XML! Yeah, that's a good idea, isn't it. Lets take a widely supported data format that many people already have, and turn it in to a completely unsupported, poorly specified fantasy format. Then you can maintain two copies of the same data! Endless fun.
It's just a symptom of the general web malaise. Am I crazy or was it once possible for real human beings to write web pages? You know, before you had to remember 90 pages of how CSS worked? The W3C these days seems to be where small minds go to die, and even TBL isn't helping.