[MegaGlide]

I do it. The fluid is lighter than water, so condensation that collects over time pools in the bottom of the master cylinder, gets pumped into your lines and is less than optimal at actuating your brakes.
I have Speed Bleeders and a Speed Bleeder Bag, so it's fairly non-heinous. If you have stock bleeders, follow the same procedure you would for bleeding brakes until all the old fluid has been pumped from the system.
Just make sure you don't let the reservoir get so low during the process that you suck air into the lines, as this will suck grief into your life because you will then need to actually bleed the brakes.

That being said, if you do it and refill the master cylinder properly when your brake pads have some miles on them, you have the potential for a paint eating mess when you install new brake pads, because the new pads will push the pistons back far enough that your master cylinder will overflow.
So, either do it right after you install new pads, or, if you do it with worn pads, remember to suck some fluid out before you push the pistons back, and top off when new pads are installed.
I would suggest using a new battery filler rubber bulb tool or a dedicated turkey baster, not a straw and your mouth. Discard the removed fluid.

Another helpful hint for living, from The Committee's almanac.