I find 10 day auctions a waste of money unless you are selling multiple items or using the listings to help bring buyers into your eBay Store. The most action on listings generally happen in the first and last 24 hours of a listing so 10 day listings show almost no action for 8 or 9 of the 10 days, and that includes getting watchers.
I have often found 5 day listings do as well or better than 7 day listings, perhaps because early bidders don't get as much of a chance to "cool off".
If you have an item that you *know* will get a lot of hits (like iPods, for instance), 3 day auctions are great for the possibility of generating a lot of heat and frantic bidding, because the 1st and last 24 hour periods are only separated by 1 day.
1 day auctions seem to be designed for fraud artists to list questionable merchandise before eBay can cancel their listings. If there was any proof that eBay is in this just for the money the 1-day auction is it. :^O
Cheers,
Ernie.