SettingProfiles also works well for these types of things. It will also allow you to silence the ringer except for calls from certain numbers in addition to the time based and location based switching and profile settings. Cheaper than locale too. Timerrific is nice too, just SP has more options.
Timeriffic has been flawless in function for me.....so much that I don't even think about it.
My biggest issue seems to be when I want to manually do something I have to "remember" how since I never touch my volume controls for anything (like going to a movie and wanting to make sure it's silenced for phone calls, txt messages, etc..).
You have to configure your profiles properly...use as few or as many as you need.