I know that an expired certificate does not automatically mean unsafe, but there is always the chance it's not the real site, and I don't take chances with my personal monetary information. I think I'll email Jeff, just to be sure.
Great advice give right below, Spa, but I would make sure the date on your computer is set properly first. I just ordered a few shirts from MGA a few days ago with no certificate warnings.
An expired certificate doesn't necessarily mean "unsafe." I set certificates at work and it does often come down to the user's computer date (month and year).
Browser and OS can also give false positives on the popups for certificates. I just checked again and Firefox / Mac (lion) has no certificate trouble there.
