Regarding vignetting, it's easy to check especially if you are using a digicam. Just test out a shot or too with a small aperture and you can see if there's vignetting. Of course you may have to download the image to your PC to see the full frame though, cos I understand the LCD on the camera body may not show the full frame, but then you can always zoom in to the corners to have a look.
Once you have a hood, use it at all times, even at night, not just when you are shooting in bright sunlight. Like I mentioned above, any light that is not directly involved with creating your image should be kept out of your lens.