David Stevens wrote:If I understand correctly, a single key would allow me to back up all 3 machines to their own individual archives.
You understand correctly.
What is the advantage of having 3 keys and a single "accessible to all machines" archive?
At this time, the primary advantage is space efficiency. For example, most of the operating system in the G4 iMac and the Mini are the same. QRecall would only store one copy of the (common parts) of the OS in the archive. Similarly, if you duplicate large iTunes or iPhoto libraries by copying them to each computer, you could have gigabytes of duplicate data.
Disadvantage: only one computer can capture to the archive at a time.
So it primarily depends on how tight your archive storage space is. I'd suggest starting with one key and three archives. See how much space the archives use. You can then decide if you're going to run out of backup storage space. You can always buy one or two additional keys later and switch to using shared archives.