Any thoughts on whether putting an item Buy It Now for a short amount of time (3, 5, 7, or 10 days) affects selling vs. 30 days.

Does it have a similar effect as ones put up for auction? 

I always use 30 days as it's simply more time for the same fee. I also use manual best offer and accept offers if good enough and just ignore lowballers. I only use auction if I have to sell or need the market to decide value. The only problem with BIN is that I often travel on business at short notice and may not be around to post immediately if an item sells.

Yeah 30 til cancelled with make offer is what I use for anything over $50.  Under $50 I dont add the make offer part.  I normally add 10% to my price when I have the best offer available.  Some people get a real kick out of saving a buck with the best offer but most of the time I get that extra 10%.  One last thing if you have a lot of the same item dont list all of them at once.  Keep the quantity low as people seem to pay more for an item when they think they might miss out on the deal.  

I tend to use a shorter duration (7 days), I tend to get more traffic and sales that way. If you have a store you get 150 free BINs per month, so as long as you don't have a ton of listings you can just let them auto relist if they don't sell.

I most often use 30 days but I have noticed that they can often stick until there is less than 10 days to go. But I do tend to price high if I am in no rush to sell.

Near Christmas I was using the 10 day option because of this. Plus the free relisting turned it into a 20 day listing.