I have enjoyed using a GPS attached to my camera for several years. Many of my photographer friends gave me lots of ribbing for using it wherever I went. That's alright - I can handle the abuse. With the GPS plugged in, all my photographs are geo-tagged. The geographic coordinates are visible on the back of my camera, and they show up in the metadata when I import the photographs into Lightroom. And a double-click on the coordinates, in Lightroom, will call up Google Maps, showing my location when the shutter was opened. Unfortunately, there was no way to enter the coordinates into the metadata of photographs that were already in the Lightroom database.
In fact, I've been taking photographs longer than the GPS satellites have existed. There certainly was no automatic capture of the metadata in my film days. But I kept records of my shooting locations on 3x5 cards that recorded the contents of each negatives, including location. I've stored those cards in a little plastic box for years.
Now, in Lightroom 4, I can rectify the lack of location data in my old photographs by using the Map Module.
This marina is located in McKay, Australia. I was there for a couple of weeks on a business trip. (Yes, I've been pretty lucky with some of my business trips.) You can see the GPS field is empty because this photo was taken long before I had a GPS attached to my camera.
Since I know where this was taken, I can zoom into the map to the location. While the map is up, I highlight the photo (or photos); right-click on the location; and Lightroom will add the location to my metadata. The orange marker is where I was standing, and the location is now in my metadata. Sweet!
When you zoom out, you can see groups of your photographs displayed. As you zoom into the groups, the photographs will be broken out of the groups to their exact locations.
So, with more than 50,000 photographs I have some work to do. I've created a smart collection that gathers all images without GPS coordinates to make this task easier. No, I won't put GPS data into every photograph. I don't need the data for model shoots, weddings, or family photographs, etc. If I'm not worried about precision, I can assign a group of photographs taken in a general vicinity and assign them all a location. For example, all my photographs taken on the grounds of Schloss Hohenschwangau, in Bavaria, can have an identical location.
I will continue to attach my GPS during my photowalks and when I visit new places. If you secretly want to join me in geo-tagging photographs, but don't want to buy a GPS, you now have the capability to enter the locations after the shoot. It's just another way to have fun with your photography. Just don't let Mark know, or he will taunt you, too. ;-)