My iPhoto is running slower and slower.

Given that an iPhoto 11 library is good for 1,000,000 images, I guess that you have a little headroom yet.

As a Test:

Hold down the option (or alt) key and launch iPhoto. From the resulting menu select 'Create Library'

Import a few pics into this new, blank library. Is the Problem repeated there?

That's not a solution but a test. How much free space do you have on the hard drive? If it's less than 10 GB that may be part of the problem.

However, based on the test give this a try: Apply the two fixes below in order as needed:

Fix #1

Launch iPhoto with the Command+Option keys held down and rebuild the library.

Since only one option can be run at a time start with Option #3, followed by #4 and then #1 as needed.

Fix #2

Using iPhoto Library Manager to Rebuild Your iPhoto Library

1 - download iPhoto Library Manager and launch.

2 - click on the Add Library button, navigate to your Home/Pictures folder and select your iPhoto Library folder.

3 - Now that the library is listed in the left hand pane of iPLM, click on your library and go to the File ➙ Rebuild Library menu option.

4 - In the next window name the new library and select the location you want it to be placed.

5 - Click on the Create button.

Note: This creates a new library based on the LIbraryData.xml file in the library and will recover Events, Albums, keywords, titles and comments. However, books, calendars, cards and slideshows will be lost. The original library will be left untouched for further attempts at fixing the problem or in case the rebuilt library is not satisfactory.

Note: if you're still running 10.8.1 update your system to the latest version, 10.8.2.

OT