Hi David,
This is pretty common in the case of workflows. When a workflow step fails, the next job in the workflow will be set to the "paused" state and all jobs downstream of the paused job will remain in the "new" state until corrective action is taken. The current query for finding jobs-ready-to-run (if tracking jobs in the database, which is automatically enabled for multiprocess Galaxy configurations) ignores 'new' state jobs whose inputs are not ready, so these jobs sitting around should not cause any harm.
--nate