I've rarely left a tip specifically for the butlers, largely because it's usually a team of butlers providing service rather than a single butler. We leave a tip for the staff overall, and assume they divide it according to whatever criteria they have for themselves. In rare instances when one person goes above and beyond, we have tipped a butler.

Let me say that I LOVE the SR butler service. It is one reason I opt for SR even when there are FS or other 5 star options available, assuming the rate/location are otherwise close. (Getting SPG points for my spend is the other reason, all other things being close/equal.) Even at a place like the Chatwal in NYC, which is Luxury Collection, I love the butler service.

For me, the unpacking and packing are sublime--I love it. They always do a great job, and I despise packing at the end of any stay.

The morning coffee service is also quite nice. We also take advantage of shoe shine and pressing more than most, I'd guess. We usually get extras thrown in over the course of our stays, too, which is a nice touch.

Usually, we get recommendations about dining options and activities from the butlers, who occasionally have the concierge confirm. But it's nice having that personal point of contact every morning with the coffee service. It also allows us to get to know the neighborhood/destination a bit better, too, as our conversations usually allow the butlers to recommend more appropriate choices for us, IMO. That depends on how much you converse with them, of course.