I verified my sites and removed the verification meta code, a few days later they show up as not verified with a message to verify them again. Strange ....
1:25 am on Oct 26, 2006 (gmt 0)
We recommend that you leave the verification file or meta tag in place after verifying because we periodically check for it. If the file or meta tag is still in place, the site remains verified. If it is not in place, we prompt for verification again. (This is to ensure that the person who verifies the site continues to own it -- sites change ownership from time to time and this verification check ensures that sites don't remain verified after they change hands.)