I would personally choose not to over complicate things and simply make this the app "for when you absolutely, positively, have to be there." If there's a possibility of cancellation, well—you're looking for another app, then. I realize this will decrease the number of times the app is used, but I'd say complicating it would be worse.

I know what you mean. Biggest difficulty was trying and make it clear to the user how the app works. The more features you add, the harder that can get.

Well in my wife's case, where work is a 30 minute drive away, there is no chance she will drive to work to shut off an alarm. Maybe a good override would be to select an alternate location close by that will let you shut off the alarm (e.g. her gym or Starbucks). That way if she's not working, she will at least do something productive instead.

Ahh multiple locations. That is a good idea.

That sounds like a great option for in app purchases.

Tweeting a photo may be a bigger motivator than just text (guessing this is not a current feature based on the screenshot provided in app store.)

Photos would definitely be cool, make it seem a bit more fun - plus writing is a lot of effort.

Would have to be careful about becoming the "Naked photo tweeter app" though.