There is an option you can set in iPhoto to import pictures from Photo Stream into your iPhoto library (Events, Photos, Places, and Faces). They stick around after the photos are gone from Photo Stream. For example, the iPhoto on this Mac still has a "Dec 2011 Photo Stream" event with pictures taken then even though the Photo Stream on this Mac only goes back to August 2012.
This is set in iPhoto > Preferences > Photo Stream. Check "My Photo Stream" and "Automatic Import" below it.
Of course, you have to be sure that iPhoto runs from time to time to gather new photos from the iCloud Photo Stream. How often it needs to run depends on how fast you roll photos off the end of the 1,000 picture limit.
Remember that Photo Stream doesn't handle movies.