Whilst poking round the net I found the Web2.0 Validator. It is a slightly irreverent site that applies a set of rules to work out how 'Web2.0y' your site is. The interesting part (to me) is that they've enabled the specification of the rules themselves to be done by the general public via del.icio.us
If you mark the Web2.0 Validator site in del.icio.us you can specify a rule in the notes field using [multiple] regular expressions in the format Some Descriptive Rule Name : /regex1/ /regex2/ … /regexN/. del.icio.us can then be queried by Web2.0 Validator and attempt to parse the rules…if it parses then it's in. In this way they are achieving a sort of distributed programming model.
In a business context, I suppose this could be used in a data warehousing system to allow managers to specify business metrics….I'm sure there are lots of other practical uses.