I have always just screwed the head onto the arrow and shot them .
Does it matter if the bladed are pointing up or down, and does it make any difference from one arrow to another if the blades are different positions?

Nope... on bigger BH's some will turn them horizontal to keep them out of focus so the archer can keep his eye on the ball so to speak, rather than being distracted by the BH in your peripheral vision.

Ever look at a Simmons Treeshark on the end of an arrow......  

what NoCams said

x3

well thats what I thought, but had a guy tell me that it made all the difference in the flight from one arrow to another, I told him he was nuts, now I will tell him that the tradgang experts confirmed it,
Larry

Doesn't matter to my tuned arrow's flight.

I have a mental problem with 2-blade heads that are positioned horizontal though. It just looks like a wing and I can imagine it flying off into the wild blue yonder.

I had an employee at a very large archery supplier/shop say the same thing to me- I replied with a cocked eyebrow...  I like to have mine canted at as close to a  2 o'clock/ 8 o'clock position just for consistency, but I certainly don't lose sleep over it.

No it does not matter for arrow flight...the arrow rotates during flight anyway.

Having said this...I always orientate mine horizontally though, so I cannot pull my BH into my hand, potentially cutting myself and so I see over (do not see) the BH.  It's purely personal preference.  I am very particular about this and make every effort to mount my BH's exactly to my liking.

Years ago G. Fred Asbell told me he mounted his BH's so they were horizontal when he canted his bow at his typical angle...that has sort of stuck with me ever since.  

Kris