Grrr! I call"Free" the F word!
In my niche, some of the products weigh ounces and cost hundreds, and others weigh 20+ pounds and cost $30.
Many competitors offer free shipping over a certain amount, usually $50. I think this is taking a toll on my sales, but I'll be darned if I will let this goad me into offering Free. (Spending $100 in advertising to make $50 might, though.)
One thing I would like to try is "Flat rate shipping over $X." Maybe cap the shipping at $5 over a certain sale amount for customer reassurance. This seems like a happier medium- I will get some revenue for shipping (which is usually MORE than the $5) without raising prices across the board in a competitive industry. I have an incentive to offer the customer to add another item to the cart. The customer will (hopefully) find the $5 (or whatever) price point acceptable especially since carts are seldom less than $100.
Personally, I am wary of the word free; it makes me look for the catch.