I have a blog using the default theme (http://www.zeigen.com/blog/ )
In navigating single pages on my blog today, I saw that the customary previous post link was no longer working on recent posts.
It worked fine previously.
It broke on one post in particular. On that post, both previous and next links appear. After that post, the previous link no longer appears.
Steps to reproduce:
1. Go to http://www.zeigen.com/blog/2009/01/plinky-linky-another-time-sinky/
2. Observe the previous post link is present.
3. Click the next post link in the upper right.
4. Observe this page does not have a previous post.
The odd thing is that it was a different page that broke previously and after I edited that post's title, a whole bunch of posts that had a working previous link no longer did.