Miles covered/time: 5000/two years
What's good: It's really comfortable and makes a massive difference to your body temperature. It may appear to be a very thin fleece but it manages to pack in a huge level of warming performance and will also go under fairly tight leathers so can be used on even really chilly winter days.
During the colder months I roll the fleece up into a very small ball and stash it at the bottom of a bag so it's always ready for use.
What's not: Nothing meaningful I can think of.