I've heard of SLUG MAIL BUT REALLY.....!!!

Thats weird, i sent mine out four days before you and everybody except one received them.

The thing about the Post office putting it in a new envelope, thats happened to me before too. Dishonest post office employees do that sometimes, searching for money that is sent by mail. My grandma received her birthday card three times with the top ripped open and taped back, and her money was gone out of it.

Did you have something protruding on it, like a bow with a metal clip? My dad sent my sisters and me a card that had metal in it and it snagged on their machines--I got mine but the envelope was torn open by the machine and the metal was missing, another sister had the same thing happen, and 2 never arrived. Since so much is automated these days, if it doesn't sit flush you run the risk of a malfunction on their end!

I do not trust post offices...

One was directly responsible for ruining some of my invitations. I had double checked the weight of each invitation. The required postage was $0.66, which I provided. However, the post office in one city thought I only had $0.46 stamps. All the invitations I sent to that city got returned. The post office stamped "Insufficient Postage" over the beautiful calligraphy. Obviously this situation was particularly infuriating because my postage was sufficient. Furthermore, I couldn't be sure who received invitations and who didn't.

Also, my calligrapher told me that one of her brides had some of her Save the Date's stolen, presumably because a post office worker thought that there was money inside. :-/

Hopefully the post offices your invitations are going through are more honest and competent. Chances are that the mail is taking longer to process due to the holiday season.