It is more dynamic with a list of trending topic and a search form.
Official announcement from blog.twitter.com:
“Twitter’s homepage is a work-in-progress. Today, we’re testing a new design that bubbles up more of the information flowing through Twitter. This builds on a series of changes starting last year when we redesigned the homepage to make search and trending topics more visible and easily accessible to everyone. With that version, we brought the power of search.twitter.com to the homepage and let people explore the value of Twitter without an account.”
Read more at blog.twitter.com