I just had dinner with Dick Hardt of Sxip. He’s about to launch Sxipper, an open-source, "learning" version of those familiar adware wallet tools. This one will be a Firefox plug-in, coming out in a couple of weeks. It's free, but (natch) there's a charge for premium services.
The basic idea is that you keep your own personal data locally, stored in your browser (by the plug-in extension, actually). Meanwhile, Sxipper reads most Web fill-in-the-blanks forms and maps their fields onto your data. (Yes, you can have multiple personas for work/home addresses, etc.) But – as anyone who has used these tools knows – they often mess up, entering your address where your name should be, and so forth. Sxipper is extensible; it lets users "map" new forms – by filling in their data, which implicitly identifies the fields – and then it stores the mapping on the Sxipper server. When user B comes to the same site, Sxipper fetches the mapping from the Sxipper server. So rather than do a lot of semantic tagging itself, Sxipper relies on user-generated metadata to parse each new form once only, and then shares the results among its users. Pretty cool.