My friend Myke Ninness likes to refer to the Magic Wand tool in Photoshop as the Tragic Wand. And it's certainly no coincidence that Photoshop CS3 features a FANTASTIC "Quick Selection tool" that now finally makes the Magic Wand tool that much more irrelevent.
However, the Magic Wand tool in Illustrator often goes unnoticed, even though it can be quite useful. For example, it can be used to fix hairline rules.
As you may know, computer programs like InDesign, QuarkXPress, and of course, Illustrator, allow you to specify a custom width, or weight, for a stroke attribute. But computers can specify any width. And designers who may want really skinny rules or lines may specify stroke weights in the order of .1 points. While it will show up on a printer, and even on a laser proof or film separations, nary a printing press in the real world would be able to hold that kind of rule. The result would most likely be that the rule wouldn't appear on a press sheet at all. The ink droplets would simply be too small to stick to the surface of the paper.
Therefore, designers, production artists, and prepress operators will never specify a stroke weight below a certain value (for me it was always .25 pt, but for others it might be .3 pt or even .5 pt). The exact value would also depend on the type of printing and the type of paper used. In any case, problems arise when you edit files because objects are constantly scaled and resized, and if Illustrator is set to scale strokes, then it's possible that some strokes will be set lower than a value you're comfortable with.
You can't use the Select > Same settings because you may have hundreds of strokes that were each scaled separately, meaning you could have hundreds of different stroke weights that could be problematic. A manual solution is to select each stroke, check its weight, and move to the next stroke. But some of us like to spend less time in the office and more time with the family. There are also some wonderful plugins that can help here, but why pay for something when you have it for free?
Double click on the Magic Wand tool in the Toolbar to open the Magic Wand palette. Expand it so that you can see all of the settings and uncheck all options except for Stroke Weight. For the tolerance, specify* your optimal stroke weight (I use .25 pt). Then, draw a new line and give it a .25 pt stroke weight. Click on the new path with the Magic Wand tool.
The result? All objects with stroke weights between 0 and .5 will become selected. You are then free to set the stroke weight for all of the selected objects to .25 pt at one time.
*I've noticed what appears to be a bug. Even if your preferences are set to use Points for Stroke Weight, the Magic Wand palette may still ask for that value in inches. To fix the problem, you'll need to also set your General measurement to Points (you can set it back after you've made the adjustment in the Magic Wand palette).