Apps have the ability to load on boot, and many apps do just that. They claim that it's so they can check for updates, or enable you to receive notifications of events. If that is the issue, rebooting won't help, as apps will load themselves right back up again. I should reiterate/clarify. I'm not suggesting that you start using a task killer regularly, and certainly not an automatic task killer. Just that you should use one as a one-shot deal because they are a good way to see what is in memory and how much resources it is using.