I love the feel of it when I'm working! I also like the slight sheen it has, very soft and subtle, kind of pearly. It's very luxurious and pretty. It doesn't knot as frequently as the cotton, and when it does get a knot, it seems easier to undo it. It is definitely stronger too - not once did my thread break, and it didn't fray as much at the part that goes through the eye of the needle either.
On the other hand, although both threads are basically the same weight, the silk seems to be very slightly thicker, which was a problem with the 3 smallest pearl sizes I use as ball joints, because I couldn't pass the thread through them as much as I would have liked.
There was also something I didn't expect: my new doll is about three quarters of an inch taller than the last one! It doesn't sound like much, but she looks a lot taller. That isn't really a problem, though, as she is still a nice size, and sits nicely in my hand. It was just a bit unexpected.
So on the whole, I liked working with the silk, and will definitely use it again in the future, when the dolls have a similar skin tone to that thread. Otherwise I will have to use the cotton, because it comes in a bunch of colors, but the silk does not.