I actually installed Taskpanel as one of the first apps when I first got my Hero, as I'd read in several places that it helps to save battery life. I got into the habit of routinely closing every app I had used when I was done with it and had apps I didn't use on the auto kill list.
My experience was that I was getting around 36 hours from a full charge with average use ie light web browsing while out and about, several phone calls, taking a few snapshots with the camera and 20+ SMS per day.
Having read elsewhere that Task killers were a waste of time and CPU cycles (they use memory and CPU time running in the background), I decided to uninstall Taskpanel and let Android manage apps like it was designed to do.
I have actually experienced an increase in battery life. My phone was last fully charged at 11PM on Monday night and is now sitting at 67% battery at 1.40PM on Wednesday. I am still using the phone as I was when Taskpanel was installed.
Take away what you will from my non-scientific experiment into battery life with and without a task manager, but I will certainly not be installing another one as it seems I was just wasting time making sure everything was closed down (my fianc