It seems Websense decided to block static.flickr.com in its latest database update #92635 on December 12th (as noted in this forum post). This is bad news for people like me who are heavy users of Flickr for managing photos, including the screenshots I post to this blog. Seems like an awful big hammer to use against the majority of those who use Flickr for the appropriate reasons.
I'm going to wait a few days before deciding whether to keep using Flickr for my blog screenshots, or start using an alternate location. I really like using Flickr for managing all of my photos and screenshots, because it gives me a single place to keep everything organized, tagged, etc.
Let's hope Websense has some common sense and does something to resolve this mistaken blockage soon.