1. A method for enabling users to track item selections during browsing of an electronic catalog, the method comprising: maintaining, on a computer system, a record of catalog items, and associated item quantities, selected by a user for purchase from the electronic catalog; and responding, by said computer system, to selection by the user of an item category of the electronic catalog by at least: identifying a plurality of catalog items in the selected item category; determining, based on said record, whether any of the plurality of catalog items in the selected item category are currently selected by the user for purchase, and in response to determining that at least one catalog items in the selected item category is currently selected by the user for purchase, merging item quantity information obtained from said record with catalog data to generate, for presentation to the user, a catalog page which identifies the plurality of items of the selected item category and which indicates, for at least one such item that is currently selected for purchase, a quantity thereof currently selected for purchase.