Web sites are getting increasingly chummy with their visitors. Already plenty of commercial, news, and other sites are storing names, e-mail addresses, and compilations of personal preferences for repeat visitors. The sites at Amazon, CDNow, Lands' End, and Dell (for just a few examples) are worth visiting to see just how far Web sites can already go in giving personalized, customized service for their customers. Technology for increased configurability is coming fast, and brings with it even more threats to your privacy. Before you start filling out all those preference forms for that sales site or news outlet, decide just how much of your personal information you want stored in someone else's computers...and distributed all over the globe via mailing lists. New kid on the market: "single sign-on services" or "universal sign-on services," Web sites that store your passwords, user IDs, even credit card numbers if you choose, and promise to keep your info secure from prying eyes. You only remember a single password. Some of these sites are Novell's www.digitalme.com/, www.ezlogin.com/, Microsoft's www.passport.com/, and www.passlogix.com/.