Bookmarklets more complex than this one may define and call functions, but they’re still all packed into a
href attribute. The lifehacker article has one that builds on this use of the
getSelection() method by looking up the selected text in an acronym dictionary.
Running bookmarklets on the page that contains them is rarely interesting, but when you keep these bookmarklets in your bookmarks menu (or, more likely, on your bookmarks toolbar), you can run them against anything, which is when they get valuable. You could drag that “this demo” link to your bookmarks toolbar and then highlight text on any web page, click that link, and see the highlighted text displayed in a message box, but you’d be better off dragging the more useful ones below to your toolbar:
search site lets you search the website of the displayed page with a minimum of keystrokes. Click it to display a search form with one field (for example, this form if you were looking at the lifehacker article), fill out that field with a string to search for, click “Go,” and Google searches that site for you.
cd .. goes to the parent directory of the displayed page’s directory.
backlink tells Google to list pages that link to the displayed page.
Other bookmarklets I use include post to del.icio.us and some of the RDFa bookmarklets that I mentioned recently. I also learned from the lifehacker article about Jesse’s Bookmarklets Site, which has many great ones. I was pleased to see (after an admittedly quick scan) that only my backlink bookmarklet above had an equivalent there—it made me feel like my others where somewhat original. I’m especially proud of the “search site” one, which is like the “site’s homepage” one with a few extra steps thrown in. I use these two every day; for example, a web search sends me to some page, I wonder “who are these guys?” and I click site’s homepage on my toolbar. Or, I get frustrated trying to find something on a site that doesn’t offer a Search feature, and I just use my own: search site.
2009-09-22 update When looking at a Wikipedia page, this one should take you to the corresponding DBpedia page: wp -> dbpedia. (If you use it on a page that you reached via redirection, you’ll get the DBpedia page about the redirection data. For example, compare the results of trying it on the http://en.wikipedia.org/wiki/Barack_Obama and the http://en.wikipedia.org/wiki/Obama Wikipedia pages.)