If you don't live in the UK you might not be familiar with Richard and Judy – that is, unless you work in the publishing business.
If you have any reason to be concerning with selling books then you undoubtedly are familiar with Richard and Judy. Their book club (a segment added a few years ago to their already popular husband-and-wife afternoon TV show) is now the UK's hottest ticket to selling books. If Richard and Judy feature a pick, it will sell and sell like crazy.
Some writers have compared Richard-and-Judy status with winning a lottery ticket. But not all publishers consider this phenomenon an unmixed blessing, as you can see from this piece in The Independent.
However, if you want to conduct your own test on the strength of the show's sway, try this little test. I'm going to guess that before today you never heard of a book called "The Resurrectionist" by James Bradley. Now wait and see how many days (weeks, months?) go by before that title appears somewhere on your horizon. It's a Richard and Judy Summer 2008 pick and estimates are that – due to the pick – it will now sell at least a quarter of a million copies.
It'll be interesting to see how long it takes before one turns up somewhere near you.