It's realy like it says. Some people have had a problem. Most do not. We don't know why! The chances are that if you are already upgraded to V3.0 then moving to 3.1.x should be fine.

But of course, take a backup of your DB in case anything happens. The problem usually manifests itself simply by a new table not being created or a new database column not being created. I have no knowledge of anyone losing data over it.

Any problems associated with the MySQL version would have manifested themselves during the upgrade so you should be OK. Fingers crossed!

Sadly, there has to be consideration of dropping support for these older database versions at some point in the future however. These are now very old and hosts should be upgrading. Newer versions offer important technology that would help both performance and stability such as sub queries, transactions and stored procedures. We are unable to make use of these important technologies at the moment to the detriment of the plugin.