There is a lot of data out there. Following on from a previous post, it's one thing to get to the data, understanding it is a just as big, if not bigger, challenge. That's where semantics, or the meaning of words comes in. Machine readable meaning. It's starting to catch on. Semantics don't have to be added explicitly, they might be able to be determined by machines in the future, but that isn't close.
Here are some of the bigger semantic efforts for the web and other documents:
Now all that's needed are some good tools or explanations as to how best add semantic meaning to existing websites. There are some getting started examples and processes for adding microformats, 'in-the-wild' examples and simplifications of RDFa for HTML.
Already the number of options are growing rapidly. Hopefully it will standardise soon, as search engines begin to put more emphasis on semantics.