What are you syncing anyway that could use that much data for jd to help? Stocks, news, weather, facebook, twitter, etc? Maybe it works for you if you sync everything hence using far more data to begin with? That could explain the mixed results. If you're trying to mitigate it on your own by syncing manually and whatnot, then using jd could use more battery than if not because it is another application running in the background... Just a theory.
When my phone is in a low signal area, it will constantly switch between 3G, 1X, and no data. That is what uses most of the battery, when I have data off but the network on it doesn't constantly switch back and forth and I find my battery life to be hugely improved. I don't sync much, I only sync facebook, twitter, flickr, and peeps once a day, two e-mail accounts once every 2 hours, and weather every 3 hours. I get through a 15 hour day with 50-60% battery life left.
