* Type: What type of bug is this? For example is it a crashing issue, a problem with localization or a matter of visual polish?
* Likelihood: How likely are users to experience the bug? For example, does everyone run into the issue or do only a few users run into it?
* Priority: Of the people who experience the bug, how badly does it affect their experience with the product?
Each metric is assigned a number, which when multiplied together produces a number representing "user pain", that is, how much pain it causes users. Bugs can then be sorted by this number, and you fix bugs from the top.
It's a shame bugzilla doesn't really offer much flexibility for stuff like this. I'm not saying this is the best way to prioritize bugs, but it would be nice to have some ability to try out different methodologies.