Google has added an element to their latest homepage test that instructs people what to do after they've entered a keyword. The sentence "Press enter to search," now appears under the box where you type in your keywords - where the old submit buttons used to be.
Here's a screenshot. (Click image for a larger view.)
The "Press enter" phrase was not seen in earlier screenshots of the homepage test. I've apparently gotten the test version lately, as I've seen the fade-in and the lack of buttons, but this is the first I've seen the "Press enter to search."