They are smaller hotels, not chains and usually with under 200 rooms. They are extremely tastefully decorated, and offer an exceptional level of personalized service.
DH and I stay at a place every year that could be described as "Boutique." They have 128 rooms, are not a chain, are a four diamond property, and offer very, very personalized guest service and stunning rooms--many individually decorated.
My guess is that the staff to guest ratio is about 1:2.5 and although the atmosphere is elegantly casual, the service is still stellar. The phone at guest services is answered on the first ring. The rooms are SPOTLESS. If you order room service it arrives quickly--hot and exactly as you ordered it. Anything that is legal they will arrange as long as you are willing to pay for it, and they will do so without a hassle. If I e-mail the concierge prior to arrival and ask her to set up the same spa treatments I had on our last visit, I know it will be done. If we want a bottle of a specific wine in the room on arrival, it will be there, and if they dont have it stocked in thier cellar, they will get it. That's the level of service we are talking about that differentiates a boutique hotel from a mass market or chain establishment.
Anne