J.P.
We have a corn-based carpet in our family room. I swear, there's not a thing that has been on it that I haven't been able to get out with just water!
I wanted the most stain-resistant carpet available, and this was so worth the extra money. We just went to a flooring place and talked at length with the salesmen.
We have a berber carpet in our basement (with very thick padding over the concrete floor so it's not cold) and I would never get that anywhere in my house again. Anything the kids run over it, wheels, cars, trains, baby strollers,action figures, dolls can pull out just one of the loops. That's not terrible in itself, but if I'm not careful with the vacuum cleaner, the brush will hook the loop and pull up the entire row of threads at once. Now, I have to vacuum that carpet without the brush which requires a ton more man-power to push the vacuum cleaner, and I don't think it gets the carpet as clean. Something I never knew before I got the carpet!