Yes it's true, though it has been a shock to everyone who follows the production of The Hobbit. This is the announcement made by Peter Jackson on his facebook page:

Peter Jackson has released the first video from the set of The Hobbit! The 10 minute video shows many scenes from preproduction, such as prop and costume design, dwarf horse and fight training, and rehearsing on the set of Bag End. The video gives great sneak peaks at the sets of Rivendell, Bag End, and the goblin caves. Be sure to check out the full video to get a chance to see your favorite actors and characters.

TheOneRing.net posted some photos of The Hobbit set earlier this week. One photos shows Andy Serkis (pictured), who will play Gollum, dressed in the familiar, if slightly updated leotard he was known to wear when playing the same role in The Lord of the Rings. Other photos show cast members Adam Brown (Ori), James Nesbitt (Bofur), and other unknown members of the cast and crew.

However, peeks at the set and actors may become even more infrequent. A video clip from 3 News in New Zealand (posted on YouTube by linuxelf1) explains that the filmmakers are taking the security slip seriously. “New security measures, including jackets and umbrellas, are being used” to hide the identities of the people walking around at the studios in Miramar. This video also offers a glimpse of some of the actors in 1930s dress at the opening of a new 3-D cinema. Director Peter Jackson steals the scene dressed as The Rocketeer.

According to stuff.co.nz, Warner Brothers has announced some new members joining the cast of The Hobbit. The studio named New Zealand actors Jeffrey Thomas and Mike Mizrahi will be playing the roles of dwarf kings Thror and Thrain, respectively. Their names have now been added to the IMDB page for the Hobbit films, and with no parenthetical comments about their parts being "rumored," I suppose we can take it as confirmed.

If you're a fan of the television show/miniseries Spartacus: Gods of the Arena, you will recognize Jeffrey Thomas as the patriarch Titus (pictured). He also had a recurring role on the series Hercules: The Legendary Journey. Though it doesn't appear that they ever shared an episode, Mike Mizrahi also had a small role in that series.

Familiar members of the cast include Sir Ian McKellen, Cate Blanchett, Andy Serkis, and Elijah Wood, all of whom will be reprising their characters from The Lord of the Rings trilogy. Martin Freeman will play Bilbo, and is joined by a large cast of dwarves, including Richard Armitage as Thorin, James Nesbitt as Bofur, and Aidan Turner and Robert Kazinsky as Kili and Fili, respectively.