I use Family Tree Maker as it is linked with Ancestry. I am using the 2009 version, but there are up to date ones available.
I try to remember to back my tree up by importing it as a gedcom file to my computer. This type of file is usually able to fit all family tree software and is compatible with Ancestry and GR which I use.
As a safe guard I also back it up on a memory stick, in case my computer fails.
Seems a lot of trouble to go through, but I don't want to loose all the work I have done!
Steven