A record number of Americans took to the Web to order holiday gifts after retailers flooded their inboxes with offers of extra discounts, free shipping and easy returns. But a storm that brought heavy winds and snow to much of the Midwest on Thursday -- the heaviest shipping day of the year -- could mean that some packages might not make it under the tree in time for Christmas. That's a headache for retailers, shippers and customers alike who already were experiencing problems because of the surge in shipping this year.