I can't begin to tell you how many purchases I have made online and for how many years. Easily 10 or more. Many of those purchases were/are with debit card. The thing you have to be wary of is to make sure its a secure website (look for the lock) and its a seller you are familiar with. I will order from Home Depot all day online but lets say its "House Depot" - no way! Never heard of 'em and I'm willing to bet their website would not be secure/encrypted. (Just making "House Depot" up as an example).

I've had one problem in where there was a charge that showed up on me from the Este Lauder warehouse (I think its in NY). I disputed the charge and of course it was promptly refunded to me in full. After research, it was discovered that only employees and family members of the employees could purchase from the warehouse and my card number was not obtained from an online transaction, rather from a local transaction I completed in person. I had that debit card cancelled and was issued a new one and never had another mishap.