E-commerce > Improving adding to cart experience

I'm in the process of building a webshop and i'm trying to optimize user experience piece by piece.

In most webshops when you add an item to the cart the shop a) reloads the screen and adds the item b) uses ajax to add item and wait for response of the server.

I'm thinking about this: When the user adds an item, the user immidiatly gets a response on screen ( item xx is added to cart + nice subtle animation ), without waiting for a server response. To me this would give the user a more fluid shopping experience.

But what about an error? Well, if the server response is an error, i could present that information to the user. Since errors should not happen often (if it did, the code needs to be improved), i think this is an acceptable trade-off.

What do you think? Are there problems i'm not aware off?