Hey, I don't really have enough experience of driving a car with CVT, but I do understand their good and bad points.

They are better on fuel, smoother to drive, easier to make and fit, and they are much lighter than a autobox.

I personally do not like that the car doesn't make the changing gear sound. They are odd to drive, and cost more to maintain, due to needing maintance more often.
They are also limited to cars with a smaller engine.

The ways to tell if your CVT is going down the toilet are:

The transmission will rev high and not do much, due to slipping.
You may smell burning, if it gets to hot.
A leaking box.
The car is slow to react to the drivers input.
Some boxes may vibrate.
A jerky ride.......

and so on :)

Cheers :) Thanks for the question. :)