I recently had the IT guys here at work wipe my hard drive and upgrade my mac to 10.8 from 10.6. And other than spending a few days getting it up and running again and spaces being jacked it is going ok.
I was using Time Machine to keep it backed up for a long time and I want to use it again on the same external drive. But I am concerned that my most recent backup from my old backups will be lost if I set it up using the same drive. Will Time Machine wipe all my old data or just the oldest stuff?