I received an email from a friend.
I’m updating my address book. Please take a moment to update me with your latest contact info. Your information is stored in my personal address book and will not be shared with anyone else.
Powered by Plaxo (No, I’m not going to link to it); a service that aims to help you sync your contact books (read Outlook). Plus, it tracks and updates changes in contact details. Details here –      
While the friend used a Netscape email ID which, frankly, I’ve not seen used much in correspondence with me, the email ID fed in to Plaxo’s servers on my behalf, is my main Yahoo! ID. One or more of the above links will tell you that Plaxo is tracking it by now.
I got an invite to Orkut – ignored. I got invites to Flickr and hi5 – ignored. Well, its not Flickr’s fault that I don’t have pics to share, but hi5 had it coming anyways.
Here’s the point – if you want to stay in touch with me, let me know through an email you have written, not generated by some script. I would be more than happy to take the time and effort to keep you updated about my contact details. Please spare my email IDs from such services. I don’t have 15-20 email IDs in reserve.