„OMG DO I NEED TO REPLACE MY HARDDISK?“
-> NO -> http://support.apple.com/kb/TS2028
„Invalid volume free block count“
Note: The volume free block count is a type of cache of the real information stored in the volume bitmap, and the count being off does not mean your volume is damaged in any way. An incorrect volume block count message (block count changed from X to Y) is an example of this type of message.
but a proper backup (i use rsync to an external drive) is NEVER a bad idea.
ALWAYS; ALWAYS ALWAYS KEEP TWO COPIES IN DIFFERENT PLACES OF THE FILES THAT YOU REALLY CARE ABOUT!
And the files you REALLY REALLY care about (pictures of family) burn them on SEVERAL DVD-Rs OF DIFFERENT BRANDS (not all last 10x years long) and store them in a place where the sun never shines…. 😉