Excellent points of course on back-ups. Many of us become complacent.
I did indeed have back-ups on external two separate external hard-drives. One problem was that I hid the most recent one from potential burglars ... and then I forgot where I had hidden it! Thus, I was not panicing, but I was definitely very angry at Family Tree Maker for tree files appearing to vanish. I have now found my "missing" external hard-drive and I shall be more diligent about back-ups. "Mea culpa" on that.
Interstingly my friend who lost the notes/citations for 7,000 records checked his back-up and they were missing from that as well - the disappearance had not been noticed at the time he made the back-up. A good reason for multiple sequential back-ups (at least three, set A, B, C so to speak.) As well, a memory stick copy of trees thrown into your safe/safety deposit box at the bank etc. I shall pass the excellent advice given by those who responded here onto my friend.
QUESTION: A major puzzle I am presently trying to sort out is why one back-up version of the main tree dated dated 2012-08-23 is 32,500 KB and the newer version (by two weeks) dated 2012-09-04 is 15,214 KB is just under HALF the size! ????????? !!!!!!!!!!!!! What is FTM up to here I wonder? Any ideas? I did NOT delete anything from the file. Both files have 4,385 people.
Once again - THANK YOU all very much for taking the time to respond so positively. :-)
Now if Family Tree Maker can just fix the problems with their software which cause trees and/or notes and citations to "vanish" the World will be a happier place. Fewer genealogists jumping off bridges. ;-)