Items on ebay that always get bids, like iMacs, will always go for the same amount a similar model did yesterday or the day before...
The person who got outbid by $5 at the last second is going to bid on the next auction that comes around. And will most likely bid within $5 of that last auction's winning bid.
Do a search for completed auctions, look for items that are very similar to what you are selling, see what the avg going price is, thats what yours will go for 99% of the time.
So, if that avg price is attractive to you, dont worry about a Buy it Now (the fee is quite high on anything $1000+) and just start the bidding at $.99, because you know its going to go for that avg price.
eBay people are fickle though, see which auctions got the highest price, look at their photos and description, what did they do that, perhaps, got them $50-250 more for their item.