Even if you manage to track down all the places some software does store
data (Firefox bookmarks, for example), then "they likely can be
re-installed. Maybe" (a) requires you still to have all the original
discs (assuming you even got them on a disc), _and_ the
passwords/keys/whatever if they are bought ones, (b) will take you
_ages_ to get them all back how you like them, unless you're one of
those frightening people who only uses a handful of prog.s and stays
near the default configuration in all of them.
Backing up - or rather imaging - the whole system is a safer bet. (And
make sure you have a bootable way of restoring from the backup without
using Windows; most backup/imaging S/W offers to make a bootable
something.) And make sure it's something that - I presume you're using 7
since you are posting here - restores 7 in such a way that 7 is happy
with itself.
I've used Acronis for several years, and have recovered
from disaster more than once (in two cases, from a
failed hard drive). I heartily agree with the idea
that an image backup is the simple way of recovering
everything. You don't have to think about what was there,
what might need to be installed, whether you still have
the source from which to install, how hard any individual
thing might be to reinstall, and so on. You just recover
the entire state of affairs, down to the last byte and its
contents.
Do I image every week or whatever? No, but I do image
after doing something "important" (would cost money or
inordinate amounts of time to re-do, or just contains
something I couldn't obtain again at all). I use two
USB-attached external drives. One: away from the
machine, immune to electrical faults and so on. Two:
away from the property, immune to fire, theft (more
likely), flood (very unlikely here, but think of
people in Calgary this morning with their machine
and local backups under a meter of muddy water),
cars crashing into house, really small asteroids).
At intervals, I swap the two drives: even a two-month
old system state is better than a boat anchor and
horrible regrets.
At more frequent intervals, I independently back up
my data on thumb drives, from which it would be easy
to become current after restoring from an image.
There are of course other imaging programs, but I'm
used to Acronis and it has saved me from total
loss more than once, the real acid test. And it
does have the bonus feature of permitting restores
of chosen files and folders.
And to repeat: imaging makes recovery so very
simple.