As a bonus, you get a valid Flickr auth_token for every signed in user. This makes writing Flickr API apps about the simplest thing ever.
Case in point, I wrote the largely mis-named photosthatmatter app last night in slightly less then 20 minutes, while waiting for dinner to simmer. Shows the most interesting photo from each for your contact in a given time period. Great for catching up on things you missed as they flowed by the first time.
YMMV, but it works for me.