I'm running 10.8.4 on my MacBook Air and Aperture was running fine until I installed the update to 3.4.5. Since that very moment the software has been unusable despite repairing the database and rebuilding it have first held down the Alt + Cmd buttons when starting the software. As soon as I try to do anything in my library, Aperture shows the spinning ball and any other open programmes (such as Mail & Safari) freeze and from the Force Quit show as Not Responding.
Now I understand most of the developers will be in San Francisco this week but it strikes me that quite a few people look to be having issues with 3.4.5 even though they have made no changes to their library in terms of adding or deleting images. Surely there is a simple fix to the bug I am experiencing.
I deleted Aperture and downloaded 3.4.5 from the App Store as a final try at solving my issues. After a few minutes of thinking about things Aperture has opened my library and I seem to be able to make adjustments to images. Many thanks for all your contributions and suggestions above. What is really frustrating is that with Version 3 being so old and having had so many updates there shouldn't be issues like this.
If and when Apple decide to go for Aperture v4 I hope they really iron out the bugs or however much people want to use their products they will see many slip away to use alternative solutions that user communities rate highly.