well I had two interviews at Downing last December and got a place for 2012 as I want to take a gap year. I'm so happy, still can't believe it.
I personally think you can't really prepare specifically for Land Economy interviews, which probably makes them some of the harder ones (as it's very relieving to come prepared, simply for your psyche). Reading the paper really does help I guess, simply try to keep up with current affairs. And I found it helpful that I read the first 500 pages of 'Economics' by Samuelson. Simply reading, not learning. Especially if you're not a native speaker like me and want to familiarize yourself with terms you generally don't need & learn. I never had Economics so I was happy that I did read parts of the book at least.
My interviews touched Economics, Law, Philosophy, Geography & Biology, so it's nearly impossible to say what you'll get. And the questions didn't have anything to do with the research interests of the interviewers. So that's not a safe heaven to speculate on.
I was asked about happiness, some statistics & graphs & maths to interpret, land conservation, the true meaning of being happy with your life, traffic, urban planning & distribution of wealth.
Oh, and about the ongoing discussion about the whole 'Land Economy is a easy bird degree for tards': I was lucky enough to speak to the Head of the Careers Office (who said it really is the best course to find a well payed job, better than Economics) & the Head of Admissions for Downing (who told me that it's, eg, much harder to get into LE at several Colleges then into Law or Economics; and LE is not even offered at all of them. It did come clearer in the 2010 & 2011 circles as more people want to study it.) I think it's just as challenging as any other course at Cambridge, most guys who post that **** aren't even in Economics, and if they are, are exactly those arrogant guys who (apparently) are enormously attracted to do E&M at Oxford or Economics at Cambridge. Quite a few you don't wanna be with. Seriously.