Here is a little grid that compares different geolocalisation technique.
| PHP GeoIP | Google Gears | Google Ajax API | Browser Geolocation | |
|---|---|---|---|---|
| Requires Javascript | No (good) | Yes | Yes | Yes |
| Requires user approval | No | Yes | No | Yes |
| Supported browsers | All (server-side) | All | All | Firefox 3.1+ and Safari 4 (or 3??) |