Since upgrading to Aperture 3, I can no longer see aperture photos in my system preferences. The "Aperture" option is there, but no photos show up. Bummer.
There is definitely something up with this. It won't work for me either.
When I *first* imported my library to A3, the "Aperture" option chooser to set a desktop image worked. It had the arrow that allowed me to browse my library. I even had set it up to pull from an Aperture 3 smart folder that I'd setup specifically for my desktop images. It was working perfectly for several hours.
But then sometime later, it just stopped working. I don't know what happened. The "Aperture" option is still there but there's no "arrow" that allows me to browse it.
Looks like this....
You can see that iPhoto still browses, but Aperture won't.

If I switch to a blank or different Aperture 3 Library, then the "arrow" comes back and it allows me to browse. It returns to looking like this...
But it won't browse my main photo Library. iTunes can still "see" it, and it's syncing photos correctly to my AppleTV and iPods, so the library itself seems ok.
I've tried the "Repair Permissions" and "Repair Database" options when starting A3 (hold down option + control), but neither had any affect. I'm debating whether to try the "Rebuild Database" option, but I don't want to do that unless I have to. And I guess I could try to rebuild my entire 60GB photo library into a new library that appears to work, but I'm not going to spend hours doing that when it may just break again later.
Anyone figure this out? It's such a minor thing, but it's pretty annoying that it doesn't work.