Noticed how you do the same things every single time you enter your home? What if that could be automated, based on Bluetooth?
The catch? It cost me a night of sleep, and I never used it after that.
A script running on my iMac would scan its surroundings for my phone's Bluetooth ID. When it found it, it created a Keynote presentation, started some music (based on my last.fm profile), and began reading my emails.
It worked great. Until at 3am, when my iMac started playing Kenny Rogers at a loud volume, with a voice over that read my latest emails. Turns out the Bluetooth connection in the bedroom was spotty enough for my iMac to think I was leaving and coming home.