Pigeon--I"m right there with you. Neither DH or I wanted to watch (though we were invited to by his pedi)DS's circ at around 36 hrs of age. That's just more than I can handle.
But to the OP: If you can handle it (and you think your kids can) go for it.
But what kind of card do you get the parents? Happy Bris Day? Do they MAKE cards for that sort of occassion? I've seen Happy Hannukuh (Chanukuh?) Cards and Bar/Bat Mitzvah cards, but never a Happy Bris Day card.
Hmm..I could start a whole new greeting card line. Cards to give parents on the day of their son's Bris...
Happy Bris Day! He didn't need that extra skin anyway. Right?

Happy Bris Day! Because it's not mutilation if it's for religious reasons.

Happy Bris Day! Because when God created the *beep*, he added an extra flap, just so the Rabbi could cut it off!

*flame suit on*
TOV