We sent out an e-mail to all of our clients the other week.
Even though the update has been out for a while and crucial, many users had not upgraded. We got a lot of tickets about clients blogs suffering because of it, so we decided to send out an e-mail.
Better for them to be safe than having to clean up the mess for when it will get exploited.
Not hard to update Wordpress either. Just to sign up to their mailing list, then literally click on your dashboard to update.