I searched the Legal stuff and didn't see anything about this but that doesn't mean it's not in there. Any insight or actual staff answers would be greatly appreciated, thanks.
More detail about my idea:
I would run the giveaway for a set time like a week or two and post on the Instructable that all current followers are eligible to win as long as they are subscribed to me by the deadline and until the winner(s) is/are chosen (which would be asap). They would also have to comment on the Instructable that they would like to be entered in the giveaway so that I know who to include in the drawing.
To choose the winner I would use a random number generator to assign numbers to each of the users who are following me and leave a comment and then use the random number generator to choose the actual winner. Another option is to just write all the names down on little pieces of paper, mix up, and blindly choose one. I'll do whichever option is the easiest but I definitely want it to be as close to random as possible.
I will mail the prize via USPS normal letter mail so I will have to ask for the mailing address of the selected winner or winners but I will not store their address or anything like that, it's only to mail the prize. I don't want to spend more than the price of a stamp so I might have to limit it to US entrants only :( but I'll look into this.
I would of course also include most of what I said here so that the requirements and selection process are clear.