StumbleUpon is testing a new feature called the "Explore Box".
"For any interest, type a word into the Explore Box, and we'll pull out great stumbles for you that match that interest," the company explained in an email.
It could be viewed as a new way to search the web. As you can see, it looks very much like a search box, only instead of a search results page, you are simply transferred to the StumbleUpon experience of stumbling through various webpages.
Obviously, you wouldn't want to use this to search for specific information like you use a search engine like Google for, but it would be more useful for searching for cool things related to certain keywords - things you may not know exist. In other words: search for when you don't know what you're really looking for.
What it does more than anything is expand the Stumbleupon experience to encompass a much broader set of topics, while allowing the user to drill down to very specific things using keywords. Perhaps before you had food listed in your topics of interest, but now you can stumble through pot roast (and see some pretty good-looking recipes, I might add).
The company is asking for feedback from testers, asking them to rank the "Explore an Interest" feature on a scale of 1 ot 10 and explain why.
If the feature makes it out of testing, it may become more important to use more keyword tagging when stumbling items.