I have encountered the following problem several times at my current job as a IxD-er without finding a satisfying solution:
"What to do when a search is executed with no input, thus an empty search query?" Concretely, this means hitting the search button next to an empty text field.
I am doubting whether this should show all results, especially if you have some filters (think of genre for music for example), or no results at all. In the latter case, an extra <return all results> button or something of the kind could be used. Somehow, giving all results with an empty box seems counter-intuitive.
On the other hand, a colleague programmer said the criterium would be how big the set of possible results is. In the case of Google, there is no sense in showing all results. In a more finite database of a specific website, this would have more sense. But now, I am looking at the article search of the NY Times, and it also shows all results, even if those are about 2,5M! http://query.nytimes.com/search/query?srchst=