Clever Apps
miniGPS for the Nokia Series 60 is a brilliant little application. I've got it setup all nicely so that the minute I enter into my work "cell stations" the phone will automatically changed my profile to "Work" - so that way I don't have to worry about my phone ringing loudly hehe.
And then when getting home it changes to General so I won't miss any calls.
The hardest part is setting up all the cells that you come across and then assigning them to groups so that your changes will work with all of the base stations near the office / home.