Selecting Items Across Multiple Pages

Every web-based application I've worked on recently requires some degree of paging when the system returns large number of search results. The reason is performance constraints. While some search engines are able to present results using an infinite scroll (see Live image search), most systems seem to bump into performance limits as to how much can be loaded into a page.

Commonly, items that are distributed over a number of pages are subject to a "Select All" command. In this situation, the following question always comes up: Do we just select the items on the current page or do we select all items across all pages?

Gmail has a nice solution to this: give the user a choice.

By default, Gmail just selects the items on the current page. But it gives you a handy link at the top of the list to select across all pages (click to see full-sized image):

Here's how it looks when items are selected across pages:

This approach doesn't completely resolve the question, though, because you must select default behavior here (select single page or select across all pages).

In a study I recently completed, I found that  users expected "Select All" to do just that--select all items across all pages. The interface we tested gave users feedback on the number of items selected, but participants still wanted to check at least one other page to confirm that everything was indeed selected. This was a system participants used on a daily basis, and a few stated that they would just do this check the first time, but would subsequently feel comfortable the system had selected absolutely everything.