i have shake and save installed and i probably wouldn't recommend leaving it running throughout the day. its great in that you just shake then click continue or turn off. continue leaves it on if you need to capture another screen. i could see it being more useful for needing to captures multiple screen layouts in a row. it gives options for jpeg, bmp, png and gif when you open it. very easy to use but...
as dannzeman said, it is very sensitive...
here is where i got it