In iPhoto '08, there are two entries in the Library section of the sidebar--Events, which splits your library according to the events you've created (or that were auto-created), and Photos, which simply shows all the photos in your library. When viewing the Photos area of the library, you can optionally show the event titles from the Events section of the library; just select View -> Event Titles, or press Shift-Command-F.
With event titles visible, you'll see them above each collection of photos, and by default, every collection is opened. If you want to collapse a collection, click the small triangle next to the event title. But what if you want to collapse all the collections? As with many things Mac, the solution lies with the Option key.
Option click on the triangle next to the event title for any non-collapsed collection, and all collections will collapse. Conversely, Option-clicking on the triangle next to a collapsed collection will expand all collections.
As to whether this will still work in iPhoto '09 or not...I guess we'll all find out in the next week or two!
This story, "Collapse Collections in IPhoto ’08’s Photos Library" was originally published by Macworld.