I have 5 different trees in FTM-2012 that I've successfully linked and maintained to Ancestry.com, but remember that notes in FTM do not upload so if you lose your file ~ you lose your notes. After reading comments from others, they've hit most of the key points and I'm sure we'd all agree - you are going to be much safer if you are more disciplined!
1) Don't forget to 'compact' your file, I do it before every sync.
2) Sync frequently (for me, every 30 minutes).
3) Back-up at least daily, but a good habit is to do it when you are getting-up for a snack or bio-break. Delete older back-ups, my practice is to save two.
4) Back-up your hard drive to an external location daily (hey, it really isn't that inconvenient). BTW, if you travel a lot, something like Carbonite is an excellent solution.
5) When the system DOES crash, reboot and/or reopen FTM then exit it formally ~ then reboot! There are times I get a message that the file is open but it really isn't, and this is the best way to tackle that.
6) Keep your anti-virus software up-to-date and run regular scans (at least weekly); IF you do get a virus and it seems all is lost - haul the PC to a professional for they have the ability to scrub-and-save, well worth the $$.
7) If using a laptop, make sure your battery has sufficient life so if there is a power failure, you have some reserve power enabling a safe exit from the application.
8) Remember that computers have a life-span and sometimes you just have to put that old broken-down work horse out in the field and get yourself a more powerful PC. As applications become more powerful, so must the PC.