This tip is not about Revit.
Sometimes we erase (and also empty 'recycle bin') data by mistake. There are lots of commercial programs available that can bring back these erased data. "PC Inspector smart recovery" is available free from download.com and can bring back data from SD cards, thumbdrives, etc. too. Very hand tool.
Recently I visited an architectural site, and even though the CEO had allowed me to photograph the building, the stupid security guard got hold of my camera and erased all the pics. Luckily I found this program and was able to unerase all the photos!