It's going to be phased in over 3 years I believe? My diesel Land Rover will be caught in 2010, as will all other Landies and 4x4's if they are diesel. 2008 is massive trucks, 2009 most trucks and bigger vehicles, 2010 for pretty much anything over 1 tonne and diesel I think? It's hard to make any exclusions for different kinds of vehicles (though new ones are because they don't pollute at all!)
What I don't know is this just like the congestion charge where it only applies Mon-Fri between certain times?
I think it is a good thing, but then I'm not planning on being in London in 2010
Most people will just find a place outside of the m25 to store their vehicle or get rid of them, which seems to be the point of the exercise I guess. Maybe even friends in France etc