Eve Myles has revealed that Series 4 of Torchwood is to start filming in January 2011.

In preperation for the filming, Eve Myles is moving to America with her family for almost 8 months! This means that we aren't going to see Torchwood on our screens till at late 2011, early 2012.
Eve said: “We’re not sure yet whether we are going to be living in Los Angeles or Canada but Torchwood is already very popular in America, I had no idea exactly how big it was until I was in Washington DC and I saw myself on the back of a bus. Weird.”
Torchwood was last on our screens in 2009 with a 5-part mini series, Children of Earth, which means the last full series was in 2008. This means that Torchwood won't have been on our screens for a full series for almost 3/4 years when it finally broadcasts!

I supose it's better late than never.