Sorry for the confusion! This is likely due to the location-based reminders feature we added recently. This
post on our blog describes the feature. This
forum post may also help explain what's going on.
Location reminders (in OmniFocus, or the new Reminders app Apple added) do have some battery impact, but Apple designed the interface we're using to provide that feature in order to minimize battery use.
That said, if you haven't installed iOS 5.0.1, installing it may help - it was aimed at fixing a battery-draining bug in the OS. (Though some folks report that Apple has
more work to do in this regard.)