Aperture gave me two bugs today. Or maybe three.
One I've seen before. I move an Event, Aperture chugs along, and the Event shows no images. There's no way to make them reappear, but if I restart Aperture they're back. It happened several times today, so I ran "Select Repair Database". I don't know if this will help.
This is, of course, a rather nasty bug. It would be easy to delete a seemingly empty project and lose all of its photos. 
My second bug concerned the drop down list of Facebook albums available from the Facebook publish dialog. Each album was repeated 4 or more times. That I fixed by deleting my Facebook account and restoring it.
There's a related Facebook bug, but this one came, I think, with a Facebook change. When publishing to Facebook Aperture's share settings are ignored. Albums are always private, you have to make them visible from Facebook. This has been broken for months, and Apple hasn't issued a fix, so I suppose it's a joint bug.
 Tip: If you configure Aperture to display the number of images in Project you'll at least see that number, even if none of the images can be seen. Still, I do wonder if I've deleted images in the past due to this old bug.
Update 3/17/2013: Subsequently I also ran permissions repair. I can't say whether it was upgrading to 10.8.3 or this work, but my OS X Aperture smart album based screen saver/slideshow has now worked for two days. I think that's a record.
It wasn't obvious at first, but I also discovered 60 thumbnail sized images in 'Rejected' folder with file names like: "4206_76697672461_1778151_n (1).jpg". They are assigned batches of dates that don't match the image date. I was able to find the five of them full sized in my Library, so I was reassured that these were truly garbage and I deleted them.
Clearly the repair process did something.
I've set a reminder in my calendar to do an Aperture database repair every four weeks as a routine preventive measure.
Update 3/21/2013: I think the library database repair MAY have helped my screensaver bug, but it didn't fix the empty folder bug. I just moved a project from one folder to another, and after the move Aperture wouldn't display its images. Again, having the image count display by the Project is a potential lifesaver. Nasty nasty bug.