Perhaps every system administrator/DBA talks about this issue...and this recommendation is based on the common sense: Make valid backups of your data.
We made backups at all level: operating system, user file system directories and the database. Because we use MyISAM and ARCHIVE engines we simply flush the table we want to backup and then copy the files to the tape.
The backup must be an automated labor that must run at different level (full, incremental and differential), and there are many good open source tools for this: we use Bacula with great results.
Why I am talking about this? this last week I must drop a temporary table with so bad luck that I dropped the wrong table (an was an aggregated historic table). Those are the moments when you say...thank goodness I have a backup!