Sweeney Todd is currently shooting at the Pinewood studios in London. Yahoo has a news article with some new bits of information ; http://news.yahoo.com/s/playbill/20070227/en_playbill/106058
The article reveals Christopher Lee's character character is "the gentleman ghost".
Also, Stephen Sondheim himself sounds pretty positive about the project: "Sometimes a story or stage production has to wait a long time until the right people come together to turn it into a motion picture. That's what has happened with Sweeney Todd and I'm excited as well as confident that it will be a first-rate and startling movie."