According to my wife's employer, I was added to her plan effective 9/1/08. Nevertheless, the carrier doesn't have a record of the change; however, they say it normally will take a few weeks to get me an insurance card and it will be retroactive.
Since my employer is about to cancel my health insurance, I am nervous about the situation. Until I get the card in hand, I will worry about being "naked" with respect to health insurance. As I learned from emergency appendix surgery earlier this year, you never know when you might need it.