iPhoto '09 Places
In addition to the "who," Apple has refined the "where" of your pictures, with the Places feature. If you have a GPS-enabled camera, such as an iPhone 3G or Nikon's Coolpix P6000 (or even the original iPhone, with its WiFi triangulation location feature), when you import photos into iPhoto, their location data will be included, and stored in the program's Places database.
If you don't have some way to add GPS data to your pictures before you import them - we use Houdah Software's HoudaGeo and a Garmin GPS to tag photos via GPX track logs - you can also add your own places to individual photos or whole groups of them via the My Places dialog box, which uses Google Maps to search and pinpoint locations.
Assigning a place to a previously untagged image is done through the My Places dialog box, which uses Google to search for location information, and displays either a street map or a satellite photo (or hybrid) of the location in question.
Once you have a number of locations configured in your photos, you can use the Places window to display maps of your photos, and you can drill down via the Browse panel to see which photos were taken where. iPhoto uses some reverse geocoding functionality, which can place many of your photos contextually in a broader "area>city>state>country" scheme, rather than the standard longitude-latitude-only scheme used by many GPS devices.
This means that iPhoto was smart enough to display all the photos we had taken in Portland, for example, even though we never tagged them by name.
As neat as all this is, there are a few areas where Places feels under-baked: there is no Undo if you are changing a location, which can wreak havoc if you've accidentally selected a group of perfectly located images.
On the flip side, as good as the My Places dialog box is, it would be great to be able to copy-and-paste location data from one photo to another (something similar to Microsoft Word's Format Painter).
Also, if you're adding locations to places in Asia some maps display the local character set (Kanji, for example), even though Google Maps will display streets and place names in English if you're accessing maps in a standard web browser such as Apple Safari.
Apple has acknowledged that this happens, saying that this is a communication issue with Google Maps, but has not offered an immediate solution.
The Places Browse panel lets you quickly get to all the photos at a location. With the reverse geocoding support, you can also view, for example, all the photos taken in France, or Portland, Oregon.