According to the Flickr blog:
Ever wanted to share private photos with friends and family without making them go through the rigamarole or opening their own Flickr account? Yes? You have? Sorry – I can’t hear you … never mind: we’ll just assume you have wanted that. Well now you can!!!
You can go to any of your sets and click "Share this set" to create a guest pass. Enter up to 50 email address and choose whether you want the recipients to also have access to other friends and family photos in your photostream and boom: it’s sharetastic. Guest passes work with secret links so you can send the link yourself or have us send it for you. When you want to reign things in a bit, you can expire the guest pass at any time.
We’re especially happy about this one since it’s the second most requested feature of all time (and work has already begun on the number one most requsted feature – we’ll eventually get ’em all).
In addition, Flickr has given new life to its mobile service which seemed to have been forgotten long time ago:
We’ve updated our long-dormant and seemingly left-for-dead mobile site with a lot of new stuff. The highlights include recent activity, recent comments, support for Y! ID based login, search, and a new easier to type URL: http://m.flickr.com. This is just the beginning, we’re planning on rolling out continuing improvements to the mobile site in the near future.
(Note for old skool members: the new mobile site, sadly, will not work for you: we’ve made the transition to supporting Yahoo! ID login exclusively for mobile. The vast majority of our users are now using Yahoo! IDs, and many of the cool features we’re working on depend on fancy-schmancy, high-tech Yahoo! infrastructure that necessitates this style of login. And, as a gentle reminder, we will be requiring Y! accounts for all Flickr.com members at some point in the future.)