Pixelsync is an iPad app that lets you transfer photos from your Aperture Library onto your iPad, where you can apply keywords, rate them, and apply labels. And then you can sync back to Aperture. It's awesome. I think of it as Aperture on my iPad for all editing work.
It is now clear that existing Pixelsync users may experience problems when upgrading to Aperture 3.3 or iPhoto 9.3. If you wish to keep using Pixelsync then I can only recommend to wait until a fix has been released that address the current problems.
Luckily, I upgraded Aperture on one Mac and still have version 3.2 on the other one, so I can continue to use Pixelmator for now.