Not that I've had much dealings with them, but as far as I can tell they are:

1. Another example of "Let's over engineer something"
2. The root of all evil
3. A practical joke
4. Totally unnecessary
5. A scapegoat to blame every driveability problem on
6. Probably the easiest part to throw at a car by mechanics without a clue
7. A guaranteed source of income for the manufacturer until the last cars with them vanish from the face of the earth

Other than that they're good things to have.