Found it, Mary's post from a while ago, glad I wasn't imagining it, perhaps someone could confirm this is still the case, would be a great way to re use excess toiletries and save on land fill!
Yes, the Salvation Army shop in PP is a great find. It's just down from the Multi-hire shop. As well as the shop selling second-hand clothes, linen, beach toys, bric-a-brac and household things, they also have a shop next door selling second hand furniture.
The staff there are really friendly and the prices are great. They are also happy to take in items that you no longer need - and that includes unused shampoo, shower soap, etc which they then donate to a refuge in Palma. There's little point taking odds & ends like that back on your flight, after all!
So, all in all, it's a great place to take unwanted items to donate for sale and also to pick up some great bargains!