The problem with metadata -- it looks like you're using it in the sense of a global data dictionary -- is that its value is generally in reuse, not short-term.

As Volunteer said, it's not helping him as a downstream developer. The project sponsor typically doesn't care what helps the downstream developer on someone else's project sometime next year. Which is why creation and maintenance of this data never gets any budgetary love.

This is clearly a case where you have to suboptimize the project for the greater good of the company. And to do that, you can't rely on the project manager. There have to be incentives from an extra-project level or it won't happen.

So let's see, in order for this to happen you need:
* recognition of the value of the metadata
* high level buy-in to that value
* a view that extends beyond the current project
* appropriate incentives to support the long view
* to maintain all these factors continuously for several years

In case I've been to subtle here, I'll say it more directly. I don't think large corporations -- the ones with the most to gain from doing this right -- are typically organized in a way that it will happen. I know I've never seen it.

When dealing with unstructured data, the user community owns the metadata. They work with IT to develop it so they can organize their business data/documents. I have not worked with Wiki technology, but we use metadata to organize items in our document management systems. The metadata provides "structure" to meet a specific business need (e.g. displaying a folder structure of documents based on the metadata). Therefore, users define, and IT provides a method where owners can add to the existing values. As users add items to the repository, the system enforces metadata assignment for all required metadata categories.

There are Metadata Repository products which can be used for the purpose. You can load the repository with Metadata ( both Technical and Business, integrated) of your Organization Manually or Automate the process ( called Scanners). Once Metadata is in the Repository, you can use it for lot of purposes, including Wiki like facility to user community.
You can do Impact Analysis, Provide Data Lineage and different kind of reports. Metadata repositories do support Web interfaces as well.