I have no idea how popular the servo library is.
Google has over 100,000 hits for Arduino Servo and there are lots of active threads here on servo topics relating to the library. Some people do roll their own servo code or use external hardware, but I think most use the Arduino servo library.
Controlling speed of movement has been mentioned occasionally on the forum, but I get the sense that this is not considered a needed capability by most.
That's not to say that people would not find it very useful if it was available.