Time zones and Localisation
I wouldn't do ip geolocation. It can be very inaccurate, especially free services. Just ask the user for zip code or state, and store it in cookie.
I'm currently storing all times in UTC, to make things easier for when I start bringing multiple sites and servers online. 
The problem comes in when translating date and datetime objects into strings in my templates and when accepting user input. 6:00PM UTC doesn't mean a whole lot to someone who is  in PST. Likewise, asking users to input times in UTC is asking for disaster. 
How can I correctly translate these values in a smart, not-error-prone way? Is there a way I can determine from the HTTP request what timezone a user is in? I really need a way to determine the user's timezone with as little effort as possible.