So for the first time in my life, I rented one of those carpet cleaners you see at the grocery story (I think it was Rug Doctor).
It was for just one room and it was basically drink stains from the kids so I didn't see a need to get the carpet cleaned by a pro.
I never used those machines and was skeptical but the wife has been asking me to do it for a while. It was about $25 for a one day rental and the cleaning solution was another $15, so about $45 with tax.
It actually worked pretty good... at first I was confused on how to use it but once I figured it out, you can watch the stains disappear (yes... I know they will probably reappear again in a few months).
Lots of sweat equity, machine was heavy, had to refill with 2 gallons of water and cleaner twice (for just one room) so I couldn't see doing this for multiple rooms. Draining the leftover cleaning solution was a pain (no instructions). But, it dried pretty fast and the carpet looked clean again.
Next time, if we don't have it pro cleaned, will probably buy one of those hand steam cleaners as it was really only needed for spots and not the entire room.
So, they do work, but they may not be worth the work/time/cost.