well, most of my cam's don't have a video option, and the one's I have that do, will only work in day time
so I never use the video option, as most pic's are night time, where I place my cams'
so if I had them on video mode, I would miss way too many things
as for how fast it fills up, that would all depend on how big a SD card you can use/use!
and I gather what the quality of the mega pix is on the camera

I think video's can be cool, but I am fine with just pic's for most sets
I would also think video modes will run your battery down faster, but thats a guess on my part!
as again I don't use the video mode much