I know a person who is a Marriott Manager and one time I asked her this very question, it was referring to the soap bars (not the shampoo) and I asked what happend to all the 1/2 used bars of soap. She said they had "buckets full of them" in housekeeping. Apparently they get donated somewhere and then melted down to make new bars of soap. She did mention that one hotel she worked at before actually re-used them, the bars were shredded into soap-dust and then used for washing of the towels as laundry detergent. So my belief is they are (or could be) often RECYCLED.

I always take my allotment of "disposable amenities" with me for future trips, especially hair conditioner to take on my overseas trips, since it often isnt provided in euro-hotels, conditioner is like rare-gold in europe. The small bottles are also very convenient for carry on given the new tsa rules.

I for one do not condone raiding the maid-cart. Its an honor thing to me, I dont want them taking my stuff when they have the opportunity to do so, so respectfully I dont take their stuff. If you really need another 3 oz of shampoo, just ask them or call the front desk.