From Common Errors In English:
Not At All!
Some of us are irritated when a grocery checker asks "Do you want any help out with that at all?"
At all is traditionally used in negative contexts: "Can't you give me any help at all?"
The current pattern of using the phrase in positive offers of help unintentionally suggests aid reluctantly given or minimal in extent.
As a way of making yourself sound less polite than you intend, it ranks right up there with "no problem" instead of "you're welcome."