I'm getting double messages sent from and recieved from my friends using handscent also. But its sporadic. Sometimes it doesn't happen for a couple of days and then it will come back for a message or 2. I've also had messages that were suppose to go to one contact get sent to another. And that has not been to pleasant explaining as to what i'm talking about. So far its been innocent chatter, but i fear the day a very wrong message goes to the wrong person lol.
chefb, if youre getting double notifications in the status bar, you have to go into the preferences of the stock mms app, and disable/uncheck notifications, and then you will only recieve the handscent notifications.