There’s currently an ongoing hiccup with logging in to Yahoo! services, including Flickr. We’re working on the issue – sorry for the inconvenience!
We’ll update this post as we have news.
Update: Things should be peachy keen again! Don’t worry, we missed you too.
Update #2: Ulp, spoke too soon! The site’s being a little bit cranky – we’re working on it.
Update #2.50349: “Hello again! I feel much better,” said flickr.com.