The main symptom is reported by people who see a large blank space, where the Followers gadget contents should display, on any blog affected.
The symptoms appear to be intermittent, and varied.
Some blog owners only report that they can't view their own Followers, others report that their readers can't view their Followers either. In some cases, Followers are visible using the dashboard "nnn Followers" link, in other cases, that display is similarly blank. In a few cases, I can see Followers using one browser, but not another, for the same blog.
And even more frustratingly, this problem will come and go. In the past 24 hours, I have observed the visibility of my Followers change maybe a dozen times.
Blogger Support has been alerted, but has not yet acknowledged the problem in Blogger Help Forum: Something Is Broken.
And please, whatever you do, ignore the reference to "uGotCrossedSon"!
(Update 2011/05/28 10:00 PDT): We have an update from Blogger Support, suggesting an initial attempt to resolve this problem.
We have released a fix for the Following issue and things should be back to normal now. I've verified this in a handful of blogs which weren't working yesterday evening.
Make sure you clear your cache and cookies too!