Andy Edmonds has a post over on the MSN Search blog entitled Tagging Feedback at MSN Search where he talks about the internal app he built that is used to track feature requests and bug reports about MSN Search.

When the MSN Search team gets feedback or bug reports, each one is "tagged" with multiple keywords/categories which can then be analyzed later by frequency. The example, Andy shows in his post is the tag "ypResults" which is used to categorize featue requests for yellow page hits as part of web search results. With this system the search team can have a simple yet effective way to keep track of their most hot button issues

Andy showed this to me a few months ago and I thought it was really cool. I'd have loved to have a system like this when I used to work on the XML team to figure out what features/bugs were most often requested by users in a quantitative way.

Below is a screenshot of the feature (names changed to protect the innocent)