Have both the zi8 and the zx3. Both take good video even in low light and I don't think are grainy. Use the zi8 more indoors and the zx3 outdoors since it can get wet. As far as a inexpensive means of taking video these things are hard to beat.
Couple of people wanted to know how the boat has been treating me. Just got back from Minnesota where it ran 87.3 on gps with about ten gallons of fuel and me in it. Altitude there was about 1350'. Some day I would like to get it to sea level and see if if would break 90.