If you are like me and have thousands of unread emails for various mailing lists cloghging up your gmail account, you can bulk delete them (rather than paging through and manually secting then deleting 100 or so at a time), by using a filter, or in my case changing the existing filter to delete any matches, then selecting the "apply to x conversations below" checkbox and updating the filter. Don't forget to uncheck the delete checkbox and update the filter again afterwards, unless you want all future matches to automatically be deleted (in which case you might be better unsubscribing!).