As a keen photographer, I remember when I went over to digital, that I was fascinated by these 'orbs'... As has been mentioned, water droplets can cause them, but also any airbourne particulate - normally when a flash is being used and the camera is focussed on another object beyond the particulate the flash light bounces off... you will normally find that a flash has been used when orbs are captured. Another thing already mentioned are these 'rods' - having accidently caught 'rod' type footage on a number of occasions, and having been able to confirm what I was videoing at the time (and what was also in the shot), they seem to be nothing more than insects with a fast moving wingspeed being caught on a camera (video) where the shutter speed creates this effect. The above is just my opinion and observations... afterall, I may be wrong ;-)