The five second test is a simple usability test that helps you measure the effectiveness of your user interfaces by getting users to look at a screen for 5 seconds, and then asking them to recall what they saw. This is something I typically do at the start of a usability test to see what users understand at a high level. Show them a screen, take it away, have them talk, ask them questions. There's more about this method at UIE. This site provides a service so you can easily do this kind of thing with users by generating a test and providing a link you can share with participants to take it. The service then emails you the results.