One of the things missed in last week's kerfuffle over OPML is how the semantic part of the semantic web is going to get driven. Let's look at two of the proponents of OPML organization for an example of the problem - and no,I don't mean this as a slam. First, Scoble, who was excited over the OPML work started by Dave Winer. Scoble's blog doesn't even have categories. Which means that, from a semantic web standpoint, his posts are lost in the ether. It's not that categories are the end-all, be-all of organization - far from it. They are kind of the bare minimum required, actually.
Categorization is hard, actually - where does a given post fit? Sure, some blog systems allow for multiple categories, but - if people won't bother to assign one, what makes you think that they'll start assigning 3 or 4?
Next, we have Dave Winer - who's posts not only don't have categories, they don't even (typically) have titles. His posts have even less of a chance of being organized in any sem-web kind of fashion. Like Scoble's posts, they end up not having any of the metadata necessary to hang additional tools off of.
Which gets us to the root problem of RDF, which isn't complexity. It's a lack of user supplied metadata. The OPML categorization scheme that is being proposed breaks up on the same set of rocks. Scoble and Winer are hardly the only people blogging without extra metadata - they are just too of the most well read bloggers doing so, and as such, they make for a good example. Let's say we wanted to use RDF (or the posited OPML scheme) to created an organized taxonomy of posts (say, over the last few weeks) of either of their blogs. We can't. Not unless we first feed the raw data of each post through a text processor which will create tag data of its own. That might be accurate; heck, I don't really know what the state of technology is in the area - but based on some of the results that come back from search engines, I'd say that it's less impressive than we'd like for for that kind of categorization.
Ultimately, the biggest blockage on the road to the semantic web is us - and I see no long term solution to that social problem.