You read in the press about how much the temperature has risen in the last 100 years. There's an interesting story in the data, but the press doesn't know it.
The data has two components: the raw measurements themselves, and a set of adjustments.
Adjustments are made for a bunch of reasons: time of observation adjustments (you didn't take a reading at exactly the same time each day), environmental changes, weather station site relocations, urbanization, etc.
An interesting question is how much of the 20th century's temperature change is due to adjustments? As it turns out, the answer is all of it.
This chart shows the before-adjustment and after-adjustment temperatures for the 20th century, super imposed. All of the warming is due to adjustments, rather than raw data. Almost all of the adjustments are for readings after 1970.
Also, via Climate Skeptic, is all you need to know to understand the Global Warming panic.
Regular readers will recognize one of the songs used here. Heh.
UPDATE 14 December 2008 20:24: You want links, we got links! Well, I don't have any, but The Unpaid Bill has all sorts of links, including a short version of the report. While I was busy snarking, he was, you know, doing useful Intarwebz link-fu.