This is my use case of multitasking : I let run a gps tracking app during hours, sometimes up to 6-8 hours. Then I use (lightly) my phone for other tasks like answering a call, etc.

My experience is that Android does this as good as Meego or Sailfish, it usually consume about 5 to 7 percentage points of battery per hour (for a comparable battery), no gaps in the recording.