Most companies with a shared refrigerator have a strict policy designed by a cunning admin to keep the fridge useful. A common approach is as follows:

Each week:

1. Ask employees to claim their items in the fridge by writing their name on it.
2. Wait 1 day.
3. Throw away any unclaimed item.

This policy ensures that the fridge only has fresh items and doesn't slowly accumulate useless items. It allows you to store and find what you need. Easy, right?

Oddly enough, most companies that also have a bug database don't have a similar policy to keep bugs fresh. Bugs slowly accumulate in the system, they grow stale (no longer reflecting the behavior of the latest version), and obscure the newer more relevant bugs. Developers aren't motivated to fix bugs since they are overwhelmed with a giant murky backlog.

Why not apply the same reasoning to your bugs? Here's a suggestion:

Every few months, clear your bug database. Let the team know that you'll be closing every bug in the system older than one month. Configure your system to mail the filer when the bug is closed and tell everyone to reopen any bug that they feel is important and that they personally vouch for.

Radical? Perhaps, but I think you'll be pleased with the results.