Brake Fluid

Anyone ever change out their brake fluid? I seem to remember the service writer asking if I wanted to flush and change mine as part of one of the regular preventative maintenance services. I figured that it was just the dealership trying to generate some extra billable cost, but lately petal seems a bit spongy. Anyone know if it could be related? I have never performed any service that would cause me to require brake bleeding, at my last oil change I asked them to check it out and they told me it was probably a booster but didn't have the part in stock. I have a hard time believing this assessment since the booster should have no bearing on soft or spongy petal.
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That's a pretty big assumption to make. I'd start by just checking the fluid level and bleeding the brakes. Changing the fluid should only be necessary if the system was unsealed for a prolonged period of time. Brake fluid is primarily alcohol, but if exposed to oxygen, it can chemically react and produce water, creating a fluid undesirable for braking. Aside from that, there shouldn't be any reason to need to flush the system.
I usually change mine when it starts to look somewhat dingy, which seems to be about every 3-5 years.

I use the Motive brake bleeder to pressurize the system. It turns it into a one man job. You just need the bottle and the correct adapter for your car to match the master cylinder. Much easier than the two man method! :)
I'm a retired Ford brake engineer and have observed through the years that (depending on the ambient humidity and geography) moisture does in fact enter the system mainly through the small atmospheric vent on the underside of the master cylinder cap seal. Most all fluids are based on propylene glycol and are hydro-scopic, and by nature will attract water. The moisture then will go to work corroding the metal system components. A periodic flush works wonders with fresh Dot 3/4. I agree with jay07 on the Motive bleeder, a great little tool. NEVER mix Dot 5 silicone fluid with Dot 3 or 4 unless an full intense flush is done prior to the fill.
Is there a trick to bleeding the clutch throwout? There's about 1/2" clearance between the transmission and the underbody and no way to get a wrench on the bleeder valve. Mine is an '05 GT 5 speed.

I'd like to know this as well. Whenever I've bled the brakes, I haven't been able to do a thing about bleeding the clutch line in this car. I've never even seen a bleeder valve under there.