Consider getting some partition imaging software. This will backup a lot
more than just drivers, but then a lot more can go wrong than just drivers.
I like Acronis True Image; others prefer Norton Ghost. For more programs,
some free, see:
http://www.majorgeeks.com/downloads3.html
As for drivers themselves, they are hardware specific, and sometimes
operating system specific. For example, your motherboard's drivers would be
of no value on a random motherboard or new PC. And, with so many devices
being built into motherboards, that applies to most drivers.
The drivers for a printer or scanner are worth keeping, since they should
work on any PC with the same operating system. However, the latest/best
versions are usually available form the manufacture's website. But, for
convenience, I do tend to save the installation packages. This can be very
important in cases where the manufacturer goes out of business, or stops
supporting a given operating system.
Drivers for video and sound card, if really separate cards and not simply
built into the motherboard, are worth downloading and saving.