It requires refactoring.
For example, when I bookmark something on delicious, I tag it with all the things I think are relevant to that site at the time. But the way I categorize sites and what things I believe to be important change over time. So the only way I can search through my bookmarks to find all the things related to a certain topic that I wasn't even aware of before is to linearly scan through all my bookmarks and re-tag them.
Is there a solution to this?