From the "question everything" file, an excellent example of why you should never trust anything without verifying it yourself: a number of conservative mailing lists are forwarding the following image comparing the size of Glen Beck's rally to Jon Stewart's:
Note the circles at the bottom, which purport to show the areas involved. The first tip-off is that the leftmost circle includes both the Lincoln Memorial and a significant distance east of the WWII Memorial - areas obviously not occupied by persons in the photograph (in fact, about a quarter of the area isn't even in the photographic evidence). On the right, the circle is somewhat arbitrary, extending quite close to the Capitol Building.
Catholicgauze has taken the time to see what's really going on here, and produced this "fair and balanced" comparison:
The rectangles denote the populated areas shown in each photo. Bear in mind that there is a giant reflecting pool in the middle of the red rectangle.
This is hardly the first time we've seen political data visualizations used to intentionally mislead people and provide obfuscate information.