This is probably the most commonly asked question! While Spacewatch® discovers and tracks asteroids, we do not calculate impact probabilities. That is the job of other institutions (Minor Planet Center, JPL NEO Office, and NEODyS). Currently, there are no known asteroids or comets that are on a collision course with the Earth in the predictable future. There are several potentially hazardous asteroids that have orbits which could make them dangerous sometime in the future. However, currently none of these objects poses a danger much above the background chance that the Earth is hit by something not yet discovered. You can check the close approach distances of all known Potentially Hazardous Asteroids (PHAs) on the Minor Planet Center's "PHA Close Approaches To The Earth" page.
Throughout Earth's history, we have been bombarded by comets and asteroids from space. Impacts have happened before, and they will happen again. It is just a matter of when. This is one of the main goals of Spacewatch®, to look for the potentially dangerous objects well before they pose a threat.