Orbs seem to spring up at about every ghost site. Whilst visiting the Oregon Vortex, a few pictures my sister and I took (with our relatively new-model digital cameras) ended up having 'orbs' in them. One of the li'l beasties was right in front of my pants.

Looks pretty orbly to me, and you have to admit, having an 'orb' photo taken at the Oregon Vortex is kind of cool. However, there were a few variables I felt needed looked into...
One person argued that if that were dust, you wouldn't be able to see the seam of my pants behind it. In my experience, I've come up with photos where you could see fine details quite easily behind a solid, out-of-focus object - like an animals's spots behind a chain-link fence. If you consider that dust is smaller and finer than a chain-link fence, it would only stand to reason that you can see detail behind it.
After returning home, I took an excursion to a very dirty, very decrepit, and almost certifiably ghost-free shed where I could take photographs in similar conditions. My photographs did not disappoint.


Taken with a flash after stirring up some dust. Orbs abound!
Note that you can see the printing on the box behind the large 'orb.'
Taken shortly afterward; no flash used.
The white line in the picture is a cord.
I also paid a visit to several ghost photo websites. Turns out that they're very well aware of dust causing false postives - in fact, some sites I visited stated they wouldn't accept 'orb' photos taken by digital cameras.