As we reported earlier, all of the location information is completely opt-in. To enable it and allow Twitter to attach geographic information to your tweets, head to the Account section of your Twitter settings and scroll down to the location section. There's a checkbox for enabling the geotagging, and a button that will allow you to delete all the historical location data from your tweets if you want to erase your tracks.
Along with enabling the geolocation support, Twitter tweaked its privacy policy to explicitly include geotagging and to remind users that what they post to Twitter is (unless protected) public in nature. In a world where tweeting can get you robbed or sued, it's a not superfluous reminder that we should participate in our own sensible privacy policies when using social media tools.