I was just senting out a mass email to my members, using the plugin from this site, and I had a problem.
For some reason, my WPMU installation tried to translate the mass mailer plugin. In the mass mailer menu page, I get buttons "Save changes" and "Reset".
I wrote my email and hit "Save changes", and the last email I wrote (like a month back) was sent out. Luckily, I had copied the text so I went in and tried again.
When hitting "Reset", the text is not reset. The only thing that changes is that the buttons are changed to a "Send" button. Sending out the email from here went well.
I don't know if this is a translation issue or if this is a problem that others has had. If someone else is running the plugin, please look at what buttons you have on the mass mailer page. I'm assuming you're running the latest version of wpmu.