To reply to my own comment below: yes it's faster than iPhoto 5. The loading time for an iPhoto library with lots of pictures (99% jpegs) is very noticeably faster. Quite nice. For me it was worth getting iLife 06 just for this -- it's finally convenient enough to actually start organizing all of my photos that have been languishing on backup disks hidden away all over creation.

I'm currently using iPhoto Library Manager to wrangle multiple libraries, but with this v6 speed boost it might even be useable if I combine all my libraries back into one mega-library. Haven't tried that yet, but it might be worth a try!