Been using Llama
and I have to say it's an excellent piece of software.
It uses mobile phone antenna towers to determine what actions to take when you enter or leave an area.
At the moment I have some areas set, (home, library, some friends places), so that when I enter them the WiFi gets turned on, when I leave it gets turned off.
At home between 2300-0700 it switches to silent, (no noise, no vibration), when I leave the area during 2300-0700 it switches to normal, (ringer + vibration). Other places between 2300-0700 it will switch to quiet, (no noise).
The developers blog is at kebabapps
where you can pick up the latest betas, (including NFC and Roaming detection).