Flickr has a helpful new way to let you find people you know who have Flickr accounts. It's called find friends, and it will tap into your Yahoo Mail, Gmail, or Windows Live Hotmail to cross check those e-mails with Flickr users. When it finds matches it serves them up in a list--all of which require you to opt them in one at a time as one of Flickr's somewhat ambiguous friends classifications.
Assuming you've got accounts for all three, the odds are good you'll be able to discover some people using Flickr you hadn't found through the service's original method that required a little more legwork of befriending people either from their profile pages or searching by single e-mail addresses.
Some Flickr users are already up in arms about the new tool and the fact that it's set as opt-out by default to let you find your friends, but this is a side effect of data portability that's unavoidable unless you're putting up barriers on each end. Matthew Rothenberg, who handles Product Strategy and Management for Flickr has come back, saying:
On the opt-out versus opt-in issue, this is something where we carefully weighed the options, and chose the default option based on what we feel would have the greatest benefit for the majority of our members. Just as we chose to make "public" the default for uploaded photos, we chose to preserve opt-out as the default for people search on Flickr.
Personally, I don't see any privacy violations going on here. You're giving up some of your personal information any time you e-mail someone with a legitimate address. I see other services rummaging through much more of my data. In this case, it's completely in your interest to seek out people you're old friends or contacts with, and the next logical step from Flickr's previous people-searching tools, which clearly weren't up to snuff.
See also: ReadWrite/Web's take on the privacy issue.