I have one right now that has been changed three times, but only with a few minutes' difference each time.
Same here!!! They have changed my flight to Orlando in May 4 TIMES!! It is driving me crazy. The first time it was by several hours, I called and told them that wasn't going to work because we had to be on ME 3 hours prior to TO and that meant getting 4 kids up at 3 am!!

They did change me to a later flight.
3 other times I was changed by a few minutes. The last time, when it changed they also changed our seat assignments. This made it so we were no where near one of our 4 year olds.

I called and they did fix it. They had to move all 6 of us and change all our seat assignments.
That being said, this is the first time JB has ever changed any of our flights and I have flown them a lot out of Portland OR, and Long Beach, CA. This has been our first flight on the east coast, (with the exception of a few PDX-BOS flights which usually occur overnight.).
Over all I am very happy with the customer service, just make sure you check your seat assignment...if that is important to you. I am really glad I caught it because it wasn't an email that said the seats changed, it just said "your flight has changed" and it had changed a few min in time. Good luck.