I'd just like to add, that on my Galaxy S, battery has remained at around 85% for the past 48 hours, in which I haven't been using the phone, even though it is still on.
I actually use my sister's old Sony Ericssion as well, and have two SIMS (one for work, and one for personal), -- one on each phone. When I haven't been using the Galaxy S, the battery drain has been minimal, which is incredible, considering that all phones will drain as long as they are on. Again, credit to Android.
What I don't get is why Google hasn't been more vocal, if these task killer programs are ineffective. Many of the top 10 downloaded apps on the marketplace are some sort of task managers/killers.
I think as long as you have "background sync" on off, these programs will have little need to run.