I actually thought of something I think I'd like to do, that I think should be doable, but having no experience with IFTTT, etc. I'm not certain.
I occasionally forget to take my cellphone with me when exiting the Model S. I thought the "If" could possibly be based on the phone sensing a disconnection from the car's bluetooth, in combination with a complete lack of motion. (One potential problem with that is I don't know how quickly the car drops the bluetooth connection with the phone when the car is turned off if there is no call in progress. Anyone know that?)
Assuming we could come up with an appropriate "If" trigger, I think some of the rest is easy, and some may be more difficult. The easy part would be to send e-mail or text messages saying, "Name left his phone in the car." In my case I'd probably send my wife a text, in case we were together, and myself an email, in case I had left my phone in the car and come in the house. What would be even better, but harder, would be if IFTTT could interface with the Tesla API, and make the car honk the horn. In fact, if the Tesla API is to be involved, the "If" trigger could probably be improved upon by also involving the car's doors becoming locked and the car being in park.
The above is just one recipe I think would be useful. I'm sure many of you are already doing lots of interesting things with IFTTT and your Teslas. So let's get this discussion going!