My wife was trying to update a page on her site, and when she hit update, she got the message saying:
Are you sure you want to navigate away from this page?
The changes you made will be lost if you navigate away from this page.
Press OK to continue, or Cancel to stay on the current page.
When clicking "ok," it reloaded the edit window for that page without saving any of the changes, and when clicking "cancel," nothing happens. I tried disabling all of the site's plugins, in case that was the problem, but it did not help. I tried editing another page, and I could do so without any problem.
I did find that I can edit this page from the HTML editor, and it's only in the visual editor that this problem occurs. On the other pages I tested, I could edit with either the visual or the HTML editor without any problem.
Please note that the link I included is essentially a commercial link, but since it's for a small, local class of very limited interest, I hope it will be obvious that I'm genuinely trying to report a WordPress 2.7 problem, and not trying some lame SPAM attempt.