It's hypothesized that the Ordovician–Silurian extiction (end of trilobites) may have been caused by a GRB. This was ~450-440 million years ago. Here's to a 1 in 500 million year event! http://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_ext...
http://arxiv.org/abs/astro-ph/0504158
When the GLAST (now James Webb Telescope) data came in, it pointed to a small (~1%) anisotropy of UHE GRBs toward high metalicity galaxies. Our model was completely isotropic. Unfortunately, we didn't have time to rework the anisotropy into our model's assumptions before our funding fell through.
... and that is the story of my brief experience as a scientist.