Re: Already been done?
I use Llama, cos it's free. It's based on phone masts, rather than Wifi, but works a treat, putting my phone on silent when i get to work, disabling wifi when i'm not in range of a known hotspot, etc.
Shame the Apple patent was filed back to 2008 - it probably means that Llama (and Tasker) are now in violation and will get sued off the market. The patent, though, seems only to refer to WLAN, GPS and bluetooth as location methods - surely most people disable these to conserve power anyway, which would make the whole idea a bit unworkable?