Unfortunately, this hint doesn't seem to work anymore under iPhoto 5!!!

Yes, this seems to be gone in iPhoto 5. The iLife designers seem to have decided that no one wants to permanently delete photos or music. However, you can permanently delete from the library from within a Smart Album, just not from within a regular album.

After searching the Apple forums I have two suggestions for how to delete from both an album and library. Which one you choose depends on how many photos need to be deleted and how they're organized. If you have just a handful these techniques may still be more effort than they're worth.

1- You can permanently delete all photos in an album by creating a Smart Album where Album is the album you want to delete. Select all the photos in that Smart Album and delete. Then delete both the Smart Album and the original album.

2- Create a keyword such as "To Trash" (or use an existing one that doesn't have any photos assigned to it). Assign that keyword to the photos you wish to delete. (An easy way to do this is to open the keyword pane and drag the photos onto the keyword.) Switch to the library and display all photos with that keyword (by clicking the keyword in the keyword pane). Select All and delete.

Don't forget to empty the trash so you can recover the disk space (it's now in the iPhoto menu).