No need to speculate, just go to Settings -> Applications -> Services. I currently have 26 running apps and 3 services (Twitter, keyboard and Google messaging).

No need to speculate, just go to Settings -> Applications -> Services. I currently have 26 running apps and 3 services (Twitter, keyboard and Google messaging). You can kill them there too. Better yet, Settings -> About phone -> Battery use. Display and Cell radio usually dominate this list.