Interesting! I could see using this tool for business research and so on -- no wonder Mary Ellen Bates finds it worth her while to know about and use. I could also see its use in a library/information center setting for patrons.
I'm sure many offerors of products and services have figured out how to tap the marketing potential of a tool like this, as well. I was paying some attention to the ads that appeared on various pages as I went through the exercise in the "23 Things" wiki page.
Authority and reliability are the crux of the question about these tools and about many of the technologies we are exploring in "23 Things." I would apply all the same criteria I use for evaluating anything I find, whether it is on the Web or elsewhere -- what can I tell or what do I know about who's supplying it? are they known? reputable? and so on.
And let's not forget the common sense factor -- known in my family as the "squint" test: when you hold it at arm's length (literally or figuratively) and look at it from a different perspective or with a different lens, does it still make sense?