PROWL  Data Backup completely saved my computer.

I had recently acquired Data Backup and was still in the trial mode in version 3.0. It was time to upgrade from OSX 10.4 to 10.5. For the first time ever, I made a clone of my entire hard drive prior to the system "upgrade and archive". I had never done this before, because Apple stuff "just works".

Well, this time it didn't work. The 10.5 installer crashed, and left behind enough garbage on the disk that I did not have enough space to do another upgrade. My only option was to "erase and install" on a currently un-bootable computer. I did the erase and install, and used the Migration Assistant (Mac) to migrate all the files from the clone back to my computer.

Everything was back to working - no data lost.

The free trial (by fire, as it turned out) clearly demonstrated the value of the program, and I bought 3.0.4.  
(Version 3.0.4)