My understanding, (subject to correction of course) is that widgets use battery power just by being on your home screen based on the fact that they are being updated. Whereas apps dont use power until you open them.
But I have some 'widgets' that dont do anything but sit there. ie:S2 calendar, sticky notes, mixzing, App Protector Pro, Appbrain sync, CardioTrainer, Catch Notes, Contact Widget, Voice Recorder Widget etc. These are all icons that come from the 'Widget' menu, so I am assume that somehow they use the battery? Or, if its not something that gets updated on a regular basis, or you set it to not update, then it wont use battery? So, are they using power and using up my battery?
Ohh, and how many widgets do you have on your screens that update? And how does it impact your battery life?