The Canon Powershot G1 X includes a built-in ND filter, like a few other cameras. You simply enable it in the menu and it reduces the light hitting the sensor. The camera also supports and adapter to add a screw on filter, so it is possible to use a standard ND filter instead.
What are the advantages and disadvantages of one type of filter compared to the other?
I already like that the built-in one is so easy to use and requires nothing to carry but its position with respect to the other lens elements is opposite. How does that affect results?