I got this tip from my local subaru club, just thought I pass it along to the good people at clubwrx. If you have salt stains on your carpets from winter salt there is an easy, cheap way to clean them. All you need is plenty of hot water, white vinegar, clean rags and a shop vac. Basically scrub the heck out of the salt stains with the hot water and vinegar, don't be shy about using lots of water either, then shop vac the water up out of the carpets. Concentrate on small areas at one time, and use plenty of water but make sure you shop vac it out. I've tried other sprays and solutions but none have worked this well, I couldn't believe how well this worked.
Oh and if your worried about the vinegar smell after, just fabreeze.