Just as an FYI: I started my battery test with a full charge at 8:28 AM on July 7th. Today, more than 48 hours later, I still have three bars of battery life. Keep in mind though that I don't do many phone calls on it - maybe 5 minutes total in the past two days. I have my Exchange email set to sync every 4 hours, and yesterday I used it for a fair bit of email.
So, all in all, I'd say the battery life on the Jack is pretty darn good.
I'm continuing my test of course and will report the final battery life I got with it...