"a seesaw plank can be a dangerous object in the hands of a mischievous child who may abruptly pull down on one end when another child is passing by the opposite end, causing the opposite end to rise quickly and potentially striking the passing child."
CNN's Business 2.0 magazine has published a list of The Next Net 25. These are the websites they say are reinventing the Web. Bloglines, Newsvine, Last.fm, Technorati and digg - all sites that I use regularly - are mentioned but there are also two or three interesting sites that were completely new to me. One of the sites CNN featured, Writely, was recently acquired by Google - a deal that BusinessWeek followed up with an good overview of Web 2.0.
Another list worth reading is DesignTechnica's guide to The Best of Web 2.0. Again, most of them are fairly well-known but there are a couple that were new to me.
Make magazine has photos of the 25 finalists in the Modern Marvels Invent Now Challenge 2006, which is run by the History Channel. There's some fascinating ideas included. I like the solar powered bus stop (top picture on the above link) best. On a (vaguely) related topic, Forbes magazine has listed the 20 most useful tools of all time.