I have always upgraded when prompted for all of the sites I am admin to. I have only upgraded on one site and now getting all sorts of problems.
Add media button does not click.
Adding a link using insert link icon in TinyMCE and it makes the page reload and I see /wp-admin/edit.php and a drafts that do not even exist on the blog. I have worked out these drafts are for an RSS feed I have - go figure how that happens!
SEO by Yoast fields no longer appears, just the heading.
I really wish I did not upgrade to this version. It was very soon after the previous one.